Adding upstream version 4.92.upstream/4.92upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3908 insertions, 0 deletions

diff --git a/src/verify.c b/src/verify.c
new file mode 100644
index 0000000..236a87c
--- /dev/null
+++ b/src/verify.c
@@ -0,0 +1,3908 @@
+/*************************************************
+*     Exim - an Internet mail transport agent    *
+*************************************************/
+
+/* Copyright (c) University of Cambridge 1995 - 2018 */
+/* See the file NOTICE for conditions of use and distribution. */
+
+/* Functions concerned with verifying things. The original code for callout
+caching was contributed by Kevin Fleming (but I hacked it around a bit). */
+
+
+#include "exim.h"
+#include "transports/smtp.h"
+
+#define CUTTHROUGH_CMD_TIMEOUT  30	/* timeout for cutthrough-routing calls */
+#define CUTTHROUGH_DATA_TIMEOUT 60	/* timeout for cutthrough-routing calls */
+static smtp_context ctctx;
+uschar ctbuffer[8192];
+
+
+/* Structure for caching DNSBL lookups */
+
+typedef struct dnsbl_cache_block {
+  time_t expiry;
+  dns_address *rhs;
+  uschar *text;
+  int rc;
+  BOOL text_set;
+} dnsbl_cache_block;
+
+
+/* Anchor for DNSBL cache */
+
+static tree_node *dnsbl_cache = NULL;
+
+
+/* Bits for match_type in one_check_dnsbl() */
+
+#define MT_NOT 1
+#define MT_ALL 2
+
+static uschar cutthrough_response(client_conn_ctx *, char, uschar **, int);
+
+
+
+/*************************************************
+*          Retrieve a callout cache record       *
+*************************************************/
+
+/* If a record exists, check whether it has expired.
+
+Arguments:
+  dbm_file          an open hints file
+  key               the record key
+  type              "address" or "domain"
+  positive_expire   expire time for positive records
+  negative_expire   expire time for negative records
+
+Returns:            the cache record if a non-expired one exists, else NULL
+*/
+
+static dbdata_callout_cache *
+get_callout_cache_record(open_db *dbm_file, const uschar *key, uschar *type,
+  int positive_expire, int negative_expire)
+{
+BOOL negative;
+int length, expire;
+time_t now;
+dbdata_callout_cache *cache_record;
+
+if (!(cache_record = dbfn_read_with_length(dbm_file, key, &length)))
+  {
+  HDEBUG(D_verify) debug_printf("callout cache: no %s record found for %s\n", type, key);
+  return NULL;
+  }
+
+/* We treat a record as "negative" if its result field is not positive, or if
+it is a domain record and the postmaster field is negative. */
+
+negative = cache_record->result != ccache_accept ||
+  (type[0] == 'd' && cache_record->postmaster_result == ccache_reject);
+expire = negative? negative_expire : positive_expire;
+now = time(NULL);
+
+if (now - cache_record->time_stamp > expire)
+  {
+  HDEBUG(D_verify) debug_printf("callout cache: %s record expired for %s\n", type, key);
+  return NULL;
+  }
+
+/* If this is a non-reject domain record, check for the obsolete format version
+that doesn't have the postmaster and random timestamps, by looking at the
+length. If so, copy it to a new-style block, replicating the record's
+timestamp. Then check the additional timestamps. (There's no point wasting
+effort if connections are rejected.) */
+
+if (type[0] == 'd' && cache_record->result != ccache_reject)
+  {
+  if (length == sizeof(dbdata_callout_cache_obs))
+    {
+    dbdata_callout_cache *new = store_get(sizeof(dbdata_callout_cache));
+    memcpy(new, cache_record, length);
+    new->postmaster_stamp = new->random_stamp = new->time_stamp;
+    cache_record = new;
+    }
+
+  if (now - cache_record->postmaster_stamp > expire)
+    cache_record->postmaster_result = ccache_unknown;
+
+  if (now - cache_record->random_stamp > expire)
+    cache_record->random_result = ccache_unknown;
+  }
+
+HDEBUG(D_verify) debug_printf("callout cache: found %s record for %s\n", type, key);
+return cache_record;
+}
+
+
+
+/* Check the callout cache.
+Options * pm_mailfrom may be modified by cache partial results.
+
+Return: TRUE if result found
+*/
+
+static BOOL
+cached_callout_lookup(address_item * addr, uschar * address_key,
+  uschar * from_address, int * opt_ptr, uschar ** pm_ptr,
+  int * yield, uschar ** failure_ptr,
+  dbdata_callout_cache * new_domain_record, int * old_domain_res)
+{
+int options = *opt_ptr;
+open_db dbblock;
+open_db *dbm_file = NULL;
+
+/* Open the callout cache database, it it exists, for reading only at this
+stage, unless caching has been disabled. */
+
+if (options & vopt_callout_no_cache)
+  {
+  HDEBUG(D_verify) debug_printf("callout cache: disabled by no_cache\n");
+  }
+else if (!(dbm_file = dbfn_open(US"callout", O_RDWR, &dbblock, FALSE)))
+  {
+  HDEBUG(D_verify) debug_printf("callout cache: not available\n");
+  }
+else
+  {
+  /* If a cache database is available see if we can avoid the need to do an
+  actual callout by making use of previously-obtained data. */
+
+  dbdata_callout_cache_address * cache_address_record;
+  dbdata_callout_cache * cache_record = get_callout_cache_record(dbm_file,
+      addr->domain, US"domain",
+      callout_cache_domain_positive_expire, callout_cache_domain_negative_expire);
+
+  /* If an unexpired cache record was found for this domain, see if the callout
+  process can be short-circuited. */
+
+  if (cache_record)
+    {
+    /* In most cases, if an early command (up to and including MAIL FROM:<>)
+    was rejected, there is no point carrying on. The callout fails. However, if
+    we are doing a recipient verification with use_sender or use_postmaster
+    set, a previous failure of MAIL FROM:<> doesn't count, because this time we
+    will be using a non-empty sender. We have to remember this situation so as
+    not to disturb the cached domain value if this whole verification succeeds
+    (we don't want it turning into "accept"). */
+
+    *old_domain_res = cache_record->result;
+
+    if (  cache_record->result == ccache_reject
+       || *from_address == 0 && cache_record->result == ccache_reject_mfnull)
+      {
+      HDEBUG(D_verify)
+	debug_printf("callout cache: domain gave initial rejection, or "
+	  "does not accept HELO or MAIL FROM:<>\n");
+      setflag(addr, af_verify_nsfail);
+      addr->user_message = US"(result of an earlier callout reused).";
+      *yield = FAIL;
+      *failure_ptr = US"mail";
+      dbfn_close(dbm_file);
+      return TRUE;
+      }
+
+    /* If a previous check on a "random" local part was accepted, we assume
+    that the server does not do any checking on local parts. There is therefore
+    no point in doing the callout, because it will always be successful. If a
+    random check previously failed, arrange not to do it again, but preserve
+    the data in the new record. If a random check is required but hasn't been
+    done, skip the remaining cache processing. */
+
+    if (options & vopt_callout_random) switch(cache_record->random_result)
+      {
+      case ccache_accept:
+	HDEBUG(D_verify)
+	  debug_printf("callout cache: domain accepts random addresses\n");
+	*failure_ptr = US"random";
+	dbfn_close(dbm_file);
+	return TRUE;     /* Default yield is OK */
+
+      case ccache_reject:
+	HDEBUG(D_verify)
+	  debug_printf("callout cache: domain rejects random addresses\n");
+	*opt_ptr = options & ~vopt_callout_random;
+	new_domain_record->random_result = ccache_reject;
+	new_domain_record->random_stamp = cache_record->random_stamp;
+	break;
+
+      default:
+	HDEBUG(D_verify)
+	  debug_printf("callout cache: need to check random address handling "
+	    "(not cached or cache expired)\n");
+	dbfn_close(dbm_file);
+	return FALSE;
+      }
+
+    /* If a postmaster check is requested, but there was a previous failure,
+    there is again no point in carrying on. If a postmaster check is required,
+    but has not been done before, we are going to have to do a callout, so skip
+    remaining cache processing. */
+
+    if (*pm_ptr)
+      {
+      if (cache_record->postmaster_result == ccache_reject)
+	{
+	setflag(addr, af_verify_pmfail);
+	HDEBUG(D_verify)
+	  debug_printf("callout cache: domain does not accept "
+	    "RCPT TO:<postmaster@domain>\n");
+	*yield = FAIL;
+	*failure_ptr = US"postmaster";
+	setflag(addr, af_verify_pmfail);
+	addr->user_message = US"(result of earlier verification reused).";
+	dbfn_close(dbm_file);
+	return TRUE;
+	}
+      if (cache_record->postmaster_result == ccache_unknown)
+	{
+	HDEBUG(D_verify)
+	  debug_printf("callout cache: need to check RCPT "
+	    "TO:<postmaster@domain> (not cached or cache expired)\n");
+	dbfn_close(dbm_file);
+	return FALSE;
+	}
+
+      /* If cache says OK, set pm_mailfrom NULL to prevent a redundant
+      postmaster check if the address itself has to be checked. Also ensure
+      that the value in the cache record is preserved (with its old timestamp).
+      */
+
+      HDEBUG(D_verify) debug_printf("callout cache: domain accepts RCPT "
+	"TO:<postmaster@domain>\n");
+      *pm_ptr = NULL;
+      new_domain_record->postmaster_result = ccache_accept;
+      new_domain_record->postmaster_stamp = cache_record->postmaster_stamp;
+      }
+    }
+
+  /* We can't give a result based on information about the domain. See if there
+  is an unexpired cache record for this specific address (combined with the
+  sender address if we are doing a recipient callout with a non-empty sender).
+  */
+
+  if (!(cache_address_record = (dbdata_callout_cache_address *)
+    get_callout_cache_record(dbm_file, address_key, US"address",
+      callout_cache_positive_expire, callout_cache_negative_expire)))
+    {
+    dbfn_close(dbm_file);
+    return FALSE;
+    }
+
+  if (cache_address_record->result == ccache_accept)
+    {
+    HDEBUG(D_verify)
+      debug_printf("callout cache: address record is positive\n");
+    }
+  else
+    {
+    HDEBUG(D_verify)
+      debug_printf("callout cache: address record is negative\n");
+    addr->user_message = US"Previous (cached) callout verification failure";
+    *failure_ptr = US"recipient";
+    *yield = FAIL;
+    }
+
+  /* Close the cache database while we actually do the callout for real. */
+
+  dbfn_close(dbm_file);
+  return TRUE;
+  }
+return FALSE;
+}
+
+
+/* Write results to callout cache
+*/
+static void
+cache_callout_write(dbdata_callout_cache * dom_rec, const uschar * domain,
+  int done, dbdata_callout_cache_address * addr_rec, uschar * address_key)
+{
+open_db dbblock;
+open_db *dbm_file = NULL;
+
+/* If we get here with done == TRUE, a successful callout happened, and yield
+will be set OK or FAIL according to the response to the RCPT command.
+Otherwise, we looped through the hosts but couldn't complete the business.
+However, there may be domain-specific information to cache in both cases.
+
+The value of the result field in the new_domain record is ccache_unknown if
+there was an error before or with MAIL FROM:, and errno was not zero,
+implying some kind of I/O error. We don't want to write the cache in that case.
+Otherwise the value is ccache_accept, ccache_reject, or ccache_reject_mfnull. */
+
+if (dom_rec->result != ccache_unknown)
+  if (!(dbm_file = dbfn_open(US"callout", O_RDWR|O_CREAT, &dbblock, FALSE)))
+    {
+    HDEBUG(D_verify) debug_printf("callout cache: not available\n");
+    }
+  else
+    {
+    (void)dbfn_write(dbm_file, domain, dom_rec,
+      (int)sizeof(dbdata_callout_cache));
+    HDEBUG(D_verify) debug_printf("wrote callout cache domain record for %s:\n"
+      "  result=%d postmaster=%d random=%d\n",
+      domain,
+      dom_rec->result,
+      dom_rec->postmaster_result,
+      dom_rec->random_result);
+    }
+
+/* If a definite result was obtained for the callout, cache it unless caching
+is disabled. */
+
+if (done  &&  addr_rec->result != ccache_unknown)
+  {
+  if (!dbm_file)
+    dbm_file = dbfn_open(US"callout", O_RDWR|O_CREAT, &dbblock, FALSE);
+  if (!dbm_file)
+    {
+    HDEBUG(D_verify) debug_printf("no callout cache available\n");
+    }
+  else
+    {
+    (void)dbfn_write(dbm_file, address_key, addr_rec,
+      (int)sizeof(dbdata_callout_cache_address));
+    HDEBUG(D_verify) debug_printf("wrote %s callout cache address record for %s\n",
+      addr_rec->result == ccache_accept ? "positive" : "negative",
+      address_key);
+    }
+  }
+
+if (dbm_file) dbfn_close(dbm_file);
+}
+
+
+/* Cutthrough-multi.  If the existing cached cutthrough connection matches
+the one we would make for a subsequent recipient, use it.  Send the RCPT TO
+and check the result, nonpipelined as it may be wanted immediately for
+recipient-verification.
+
+It seems simpler to deal with this case separately from the main callout loop.
+We will need to remember it has sent, or not, so that rcpt-acl tail code
+can do it there for the non-rcpt-verify case.  For this we keep an addresscount.
+
+Return: TRUE for a definitive result for the recipient
+*/
+static int
+cutthrough_multi(address_item * addr, host_item * host_list,
+  transport_feedback * tf, int * yield)
+{
+BOOL done = FALSE;
+host_item * host;
+
+if (addr->transport == cutthrough.addr.transport)
+  for (host = host_list; host; host = host->next)
+    if (Ustrcmp(host->address, cutthrough.host.address) == 0)
+      {
+      int host_af;
+      uschar *interface = NULL;  /* Outgoing interface to use; NULL => any */
+      int port = 25;
+
+      deliver_host = host->name;
+      deliver_host_address = host->address;
+      deliver_host_port = host->port;
+      deliver_domain = addr->domain;
+      transport_name = addr->transport->name;
+
+      host_af = Ustrchr(host->address, ':') ? AF_INET6 : AF_INET;
+
+      if (  !smtp_get_interface(tf->interface, host_af, addr, &interface,
+	      US"callout")
+	 || !smtp_get_port(tf->port, addr, &port, US"callout")
+	 )
+	log_write(0, LOG_MAIN|LOG_PANIC, "<%s>: %s", addr->address,
+	  addr->message);
+
+      smtp_port_for_connect(host, port);
+
+      if (  (  interface == cutthrough.interface
+	    || (  interface
+	       && cutthrough.interface
+	       && Ustrcmp(interface, cutthrough.interface) == 0
+	    )  )
+	 && host->port == cutthrough.host.port
+	 )
+	{
+	uschar * resp = NULL;
+
+	/* Match!  Send the RCPT TO, set done from the response */
+	done =
+	     smtp_write_command(&ctctx, SCMD_FLUSH, "RCPT TO:<%.1000s>\r\n",
+	      transport_rcpt_address(addr,
+		 addr->transport->rcpt_include_affixes)) >= 0
+	  && cutthrough_response(&cutthrough.cctx, '2', &resp,
+	      CUTTHROUGH_DATA_TIMEOUT) == '2';
+
+	/* This would go horribly wrong if a callout fail was ignored by ACL.
+	We punt by abandoning cutthrough on a reject, like the
+	first-rcpt does. */
+
+	if (done)
+	  {
+	  address_item * na = store_get(sizeof(address_item));
+	  *na = cutthrough.addr;
+	  cutthrough.addr = *addr;
+	  cutthrough.addr.host_used = &cutthrough.host;
+	  cutthrough.addr.next = na;
+
+	  cutthrough.nrcpt++;
+	  }
+	else
+	  {
+	  cancel_cutthrough_connection(TRUE, US"recipient rejected");
+	  if (!resp || errno == ETIMEDOUT)
+	    {
+	    HDEBUG(D_verify) debug_printf("SMTP timeout\n");
+	    }
+	  else if (errno == 0)
+	    {
+	    if (*resp == 0)
+	      Ustrcpy(resp, US"connection dropped");
+
+	    addr->message =
+	      string_sprintf("response to \"%s\" was: %s",
+		big_buffer, string_printing(resp));
+
+	    addr->user_message =
+	      string_sprintf("Callout verification failed:\n%s", resp);
+
+	    /* Hard rejection ends the process */
+
+	    if (resp[0] == '5')   /* Address rejected */
+	      {
+	      *yield = FAIL;
+	      done = TRUE;
+	      }
+	    }
+	  }
+	}
+      break;	/* host_list */
+      }
+if (!done)
+  cancel_cutthrough_connection(TRUE, US"incompatible connection");
+return done;
+}
+
+
+/*************************************************
+*      Do callout verification for an address    *
+*************************************************/
+
+/* This function is called from verify_address() when the address has routed to
+a host list, and a callout has been requested. Callouts are expensive; that is
+why a cache is used to improve the efficiency.
+
+Arguments:
+  addr              the address that's been routed
+  host_list         the list of hosts to try
+  tf                the transport feedback block
+
+  ifstring          "interface" option from transport, or NULL
+  portstring        "port" option from transport, or NULL
+  protocolstring    "protocol" option from transport, or NULL
+  callout           the per-command callout timeout
+  callout_overall   the overall callout timeout (if < 0 use 4*callout)
+  callout_connect   the callout connection timeout (if < 0 use callout)
+  options           the verification options - these bits are used:
+                      vopt_is_recipient => this is a recipient address
+                      vopt_callout_no_cache => don't use callout cache
+                      vopt_callout_fullpm => if postmaster check, do full one
+                      vopt_callout_random => do the "random" thing
+                      vopt_callout_recipsender => use real sender for recipient
+                      vopt_callout_recippmaster => use postmaster for recipient
+		      vopt_callout_hold         => lazy close connection
+  se_mailfrom         MAIL FROM address for sender verify; NULL => ""
+  pm_mailfrom         if non-NULL, do the postmaster check with this sender
+
+Returns:            OK/FAIL/DEFER
+*/
+
+static int
+do_callout(address_item *addr, host_item *host_list, transport_feedback *tf,
+  int callout, int callout_overall, int callout_connect, int options,
+  uschar *se_mailfrom, uschar *pm_mailfrom)
+{
+int yield = OK;
+int old_domain_cache_result = ccache_accept;
+BOOL done = FALSE;
+uschar *address_key;
+uschar *from_address;
+uschar *random_local_part = NULL;
+const uschar *save_deliver_domain = deliver_domain;
+uschar **failure_ptr = options & vopt_is_recipient
+  ? &recipient_verify_failure : &sender_verify_failure;
+dbdata_callout_cache new_domain_record;
+dbdata_callout_cache_address new_address_record;
+time_t callout_start_time;
+
+new_domain_record.result = ccache_unknown;
+new_domain_record.postmaster_result = ccache_unknown;
+new_domain_record.random_result = ccache_unknown;
+
+memset(&new_address_record, 0, sizeof(new_address_record));
+
+/* For a recipient callout, the key used for the address cache record must
+include the sender address if we are using the real sender in the callout,
+because that may influence the result of the callout. */
+
+if (options & vopt_is_recipient)
+  if (options & vopt_callout_recipsender)
+    {
+    from_address = sender_address;
+    address_key = string_sprintf("%s/<%s>", addr->address, sender_address);
+    if (cutthrough.delivery) options |= vopt_callout_no_cache;
+    }
+  else if (options & vopt_callout_recippmaster)
+    {
+    from_address = string_sprintf("postmaster@%s", qualify_domain_sender);
+    address_key = string_sprintf("%s/<postmaster@%s>", addr->address,
+      qualify_domain_sender);
+    }
+  else
+    {
+    from_address = US"";
+    address_key = addr->address;
+    }
+
+/* For a sender callout, we must adjust the key if the mailfrom address is not
+empty. */
+
+else
+  {
+  from_address = se_mailfrom ? se_mailfrom : US"";
+  address_key = *from_address
+    ? string_sprintf("%s/<%s>", addr->address, from_address) : addr->address;
+  }
+
+if (cached_callout_lookup(addr, address_key, from_address,
+      &options, &pm_mailfrom, &yield, failure_ptr,
+      &new_domain_record, &old_domain_cache_result))
+  {
+  cancel_cutthrough_connection(TRUE, US"cache-hit");
+  goto END_CALLOUT;
+  }
+
+if (!addr->transport)
+  {
+  HDEBUG(D_verify) debug_printf("cannot callout via null transport\n");
+  }
+else if (Ustrcmp(addr->transport->driver_name, "smtp") != 0)
+  log_write(0, LOG_MAIN|LOG_PANIC|LOG_CONFIG_FOR, "callout transport '%s': %s is non-smtp",
+    addr->transport->name, addr->transport->driver_name);
+else
+  {
+  smtp_transport_options_block *ob =
+    (smtp_transport_options_block *)addr->transport->options_block;
+  host_item * host;
+
+  /* The information wasn't available in the cache, so we have to do a real
+  callout and save the result in the cache for next time, unless no_cache is set,
+  or unless we have a previously cached negative random result. If we are to test
+  with a random local part, ensure that such a local part is available. If not,
+  log the fact, but carry on without randomising. */
+
+  if (options & vopt_callout_random  &&  callout_random_local_part)
+    if (!(random_local_part = expand_string(callout_random_local_part)))
+      log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand "
+        "callout_random_local_part: %s", expand_string_message);
+
+  /* Default the connect and overall callout timeouts if not set, and record the
+  time we are starting so that we can enforce it. */
+
+  if (callout_overall < 0) callout_overall = 4 * callout;
+  if (callout_connect < 0) callout_connect = callout;
+  callout_start_time = time(NULL);
+
+  /* Before doing a real callout, if this is an SMTP connection, flush the SMTP
+  output because a callout might take some time. When PIPELINING is active and
+  there are many recipients, the total time for doing lots of callouts can add up
+  and cause the client to time out. So in this case we forgo the PIPELINING
+  optimization. */
+
+  if (smtp_out && !f.disable_callout_flush) mac_smtp_fflush();
+
+  clearflag(addr, af_verify_pmfail);  /* postmaster callout flag */
+  clearflag(addr, af_verify_nsfail);  /* null sender callout flag */
+
+/* cutthrough-multi: if a nonfirst rcpt has the same routing as the first,
+and we are holding a cutthrough conn open, we can just append the rcpt to
+that conn for verification purposes (and later delivery also).  Simplest
+coding means skipping this whole loop and doing the append separately.  */
+
+  /* Can we re-use an open cutthrough connection? */
+  if (  cutthrough.cctx.sock >= 0
+     && (options & (vopt_callout_recipsender | vopt_callout_recippmaster))
+	== vopt_callout_recipsender
+     && !random_local_part
+     && !pm_mailfrom
+     )
+    done = cutthrough_multi(addr, host_list, tf, &yield);
+
+  /* If we did not use a cached connection, make connections to the hosts
+  and do real callouts. The list of hosts is passed in as an argument. */
+
+  for (host = host_list; host && !done; host = host->next)
+    {
+    int host_af;
+    int port = 25;
+    uschar *interface = NULL;  /* Outgoing interface to use; NULL => any */
+    smtp_context sx;
+
+    if (!host->address)
+      {
+      DEBUG(D_verify) debug_printf("no IP address for host name %s: skipping\n",
+        host->name);
+      continue;
+      }
+
+    /* Check the overall callout timeout */
+
+    if (time(NULL) - callout_start_time >= callout_overall)
+      {
+      HDEBUG(D_verify) debug_printf("overall timeout for callout exceeded\n");
+      break;
+      }
+
+    /* Set IPv4 or IPv6 */
+
+    host_af = Ustrchr(host->address, ':') ? AF_INET6 : AF_INET;
+
+    /* Expand and interpret the interface and port strings. The latter will not
+    be used if there is a host-specific port (e.g. from a manualroute router).
+    This has to be delayed till now, because they may expand differently for
+    different hosts. If there's a failure, log it, but carry on with the
+    defaults. */
+
+    deliver_host = host->name;
+    deliver_host_address = host->address;
+    deliver_host_port = host->port;
+    deliver_domain = addr->domain;
+    transport_name = addr->transport->name;
+
+    if (  !smtp_get_interface(tf->interface, host_af, addr, &interface,
+            US"callout")
+       || !smtp_get_port(tf->port, addr, &port, US"callout")
+       )
+      log_write(0, LOG_MAIN|LOG_PANIC, "<%s>: %s", addr->address,
+        addr->message);
+
+    sx.addrlist = addr;
+    sx.conn_args.host = host;
+    sx.conn_args.host_af = host_af,
+    sx.port = port;
+    sx.conn_args.interface = interface;
+    sx.helo_data = tf->helo_data;
+    sx.conn_args.tblock = addr->transport;
+    sx.verify = TRUE;
+
+tls_retry_connection:
+    /* Set the address state so that errors are recorded in it */
+
+    addr->transport_return = PENDING_DEFER;
+    ob->connect_timeout = callout_connect;
+    ob->command_timeout = callout;
+
+    /* Get the channel set up ready for a message (MAIL FROM being the next
+    SMTP command to send.  If we tried TLS but it failed, try again without
+    if permitted */
+
+    yield = smtp_setup_conn(&sx, FALSE);
+#ifdef SUPPORT_TLS
+    if (  yield == DEFER
+       && addr->basic_errno == ERRNO_TLSFAILURE
+       && ob->tls_tempfail_tryclear
+       && verify_check_given_host(CUSS &ob->hosts_require_tls, host) != OK
+       )
+      {
+      log_write(0, LOG_MAIN,
+	"%s: callout unencrypted to %s [%s] (not in hosts_require_tls)",
+	addr->message, host->name, host->address);
+      addr->transport_return = PENDING_DEFER;
+      yield = smtp_setup_conn(&sx, TRUE);
+      }
+#endif
+    if (yield != OK)
+      {
+      errno = addr->basic_errno;
+      transport_name = NULL;
+      deliver_host = deliver_host_address = NULL;
+      deliver_domain = save_deliver_domain;
+
+      /* Failure to accept HELO is cached; this blocks the whole domain for all
+      senders. I/O errors and defer responses are not cached. */
+
+      if (yield == FAIL && (errno == 0 || errno == ERRNO_SMTPCLOSED))
+	{
+	setflag(addr, af_verify_nsfail);
+	new_domain_record.result = ccache_reject;
+	done = TRUE;
+	}
+      else
+	done = FALSE;
+      goto no_conn;
+      }
+
+    /* If we needed to authenticate, smtp_setup_conn() did that.  Copy
+    the AUTH info for logging */
+
+    addr->authenticator = client_authenticator;
+    addr->auth_id = client_authenticated_id;
+
+    sx.from_addr = from_address;
+    sx.first_addr = sx.sync_addr = addr;
+    sx.ok = FALSE;			/*XXX these 3 last might not be needed for verify? */
+    sx.send_rset = TRUE;
+    sx.completed_addr = FALSE;
+
+    new_domain_record.result = old_domain_cache_result == ccache_reject_mfnull
+      ? ccache_reject_mfnull : ccache_accept;
+
+    /* Do the random local part check first. Temporarily replace the recipient
+    with the "random" value */
+
+    if (random_local_part)
+      {
+      uschar * main_address = addr->address;
+      const uschar * rcpt_domain = addr->domain;
+
+#ifdef SUPPORT_I18N
+      uschar * errstr = NULL;
+      if (  testflag(addr, af_utf8_downcvt)
+	 && (rcpt_domain = string_domain_utf8_to_alabel(rcpt_domain,
+				    &errstr), errstr)
+	 )
+	{
+	addr->message = errstr;
+	errno = ERRNO_EXPANDFAIL;
+	setflag(addr, af_verify_nsfail);
+	done = FALSE;
+	rcpt_domain = US"";  /*XXX errorhandling! */
+	}
+#endif
+
+      /* This would be ok for 1st rcpt of a cutthrough (the case handled here;
+      subsequents are done in cutthrough_multi()), but no way to
+      handle a subsequent because of the RSET vaporising the MAIL FROM.
+      So refuse to support any.  Most cutthrough use will not involve
+      random_local_part, so no loss. */
+      cancel_cutthrough_connection(TRUE, US"random-recipient");
+
+      addr->address = string_sprintf("%s@%.1000s",
+				    random_local_part, rcpt_domain);
+      done = FALSE;
+
+      /* If accepted, we aren't going to do any further tests below.
+      Otherwise, cache a real negative response, and get back to the right
+      state to send RCPT. Unless there's some problem such as a dropped
+      connection, we expect to succeed, because the commands succeeded above.
+      However, some servers drop the connection after responding to an
+      invalid recipient, so on (any) error we drop and remake the connection.
+      XXX We don't care about that for postmaster_full.  Should we?
+
+      XXX could we add another flag to the context, and have the common
+      code emit the RSET too?  Even pipelined after the RCPT...
+      Then the main-verify call could use it if there's to be a subsequent
+      postmaster-verify.
+      The sync_responses() would need to be taught about it and we'd
+      need another return code filtering out to here.
+
+      Avoid using a SIZE option on the MAIL for all random-rcpt checks.
+      */
+
+      sx.avoid_option = OPTION_SIZE;
+
+      /* Remember when we last did a random test */
+      new_domain_record.random_stamp = time(NULL);
+
+      if (smtp_write_mail_and_rcpt_cmds(&sx, &yield) == 0)
+	switch(addr->transport_return)
+	  {
+	  case PENDING_OK:	/* random was accepted, unfortunately */
+	    new_domain_record.random_result = ccache_accept;
+	    yield = OK;		/* Only usable verify result we can return */
+	    done = TRUE;
+	    *failure_ptr = US"random";
+	    goto no_conn;
+	  case FAIL:		/* rejected: the preferred result */
+	    new_domain_record.random_result = ccache_reject;
+	    sx.avoid_option = 0;
+
+	    /* Between each check, issue RSET, because some servers accept only
+	    one recipient after MAIL FROM:<>.
+	    XXX We don't care about that for postmaster_full.  Should we? */
+
+	    if ((done =
+	      smtp_write_command(&sx, SCMD_FLUSH, "RSET\r\n") >= 0 &&
+	      smtp_read_response(&sx, sx.buffer, sizeof(sx.buffer), '2', callout)))
+	      break;
+
+	    HDEBUG(D_acl|D_v)
+	      debug_printf_indent("problem after random/rset/mfrom; reopen conn\n");
+	    random_local_part = NULL;
+#ifdef SUPPORT_TLS
+	    tls_close(sx.cctx.tls_ctx, TLS_SHUTDOWN_NOWAIT);
+#endif
+	    HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP(close)>>\n");
+	    (void)close(sx.cctx.sock);
+	    sx.cctx.sock = -1;
+#ifndef DISABLE_EVENT
+	    (void) event_raise(addr->transport->event_action,
+			      US"tcp:close", NULL);
+#endif
+	    addr->address = main_address;
+	    addr->transport_return = PENDING_DEFER;
+	    sx.first_addr = sx.sync_addr = addr;
+	    sx.ok = FALSE;
+	    sx.send_rset = TRUE;
+	    sx.completed_addr = FALSE;
+	    goto tls_retry_connection;
+	  case DEFER:		/* 4xx response to random */
+	    break;		/* Just to be clear. ccache_unknown, !done. */
+	  }
+
+      /* Re-setup for main verify, or for the error message when failing */
+      addr->address = main_address;
+      addr->transport_return = PENDING_DEFER;
+      sx.first_addr = sx.sync_addr = addr;
+      sx.ok = FALSE;
+      sx.send_rset = TRUE;
+      sx.completed_addr = FALSE;
+      }
+    else
+      done = TRUE;
+
+    /* Main verify.  For rcpt-verify use SIZE if we know it and we're not cacheing;
+    for sndr-verify never use it. */
+
+    if (done)
+      {
+      if (!(options & vopt_is_recipient  &&  options & vopt_callout_no_cache))
+	sx.avoid_option = OPTION_SIZE;
+
+      done = FALSE;
+      switch(smtp_write_mail_and_rcpt_cmds(&sx, &yield))
+	{
+	case 0:  switch(addr->transport_return)	/* ok so far */
+		    {
+		    case PENDING_OK:  done = TRUE;
+				      new_address_record.result = ccache_accept;
+				      break;
+		    case FAIL:	    done = TRUE;
+				      yield = FAIL;
+				      *failure_ptr = US"recipient";
+				      new_address_record.result = ccache_reject;
+				      break;
+		    default:	    break;
+		    }
+		  break;
+
+	case -1:				/* MAIL response error */
+		  *failure_ptr = US"mail";
+		  if (errno == 0 && sx.buffer[0] == '5')
+		    {
+		    setflag(addr, af_verify_nsfail);
+		    if (from_address[0] == 0)
+		      new_domain_record.result = ccache_reject_mfnull;
+		    }
+		  break;
+						/* non-MAIL read i/o error */
+						/* non-MAIL response timeout */
+						/* internal error; channel still usable */
+	default:  break;			/* transmit failed */
+	}
+      }
+
+    addr->auth_sndr = client_authenticated_sender;
+
+    deliver_host = deliver_host_address = NULL;
+    deliver_domain = save_deliver_domain;
+
+    /* Do postmaster check if requested; if a full check is required, we
+    check for RCPT TO:<postmaster> (no domain) in accordance with RFC 821. */
+
+    if (done && pm_mailfrom)
+      {
+      /* Could possibly shift before main verify, just above, and be ok
+      for cutthrough.  But no way to handle a subsequent rcpt, so just
+      refuse any */
+      cancel_cutthrough_connection(TRUE, US"postmaster verify");
+      HDEBUG(D_acl|D_v) debug_printf_indent("Cutthrough cancelled by presence of postmaster verify\n");
+
+      done = smtp_write_command(&sx, SCMD_FLUSH, "RSET\r\n") >= 0
+          && smtp_read_response(&sx, sx.buffer, sizeof(sx.buffer), '2', callout);
+
+      if (done)
+	{
+	uschar * main_address = addr->address;
+
+	/*XXX oops, affixes */
+	addr->address = string_sprintf("postmaster@%.1000s", addr->domain);
+	addr->transport_return = PENDING_DEFER;
+
+	sx.from_addr = pm_mailfrom;
+	sx.first_addr = sx.sync_addr = addr;
+	sx.ok = FALSE;
+	sx.send_rset = TRUE;
+	sx.completed_addr = FALSE;
+	sx.avoid_option = OPTION_SIZE;
+
+	if(  smtp_write_mail_and_rcpt_cmds(&sx, &yield) == 0
+	  && addr->transport_return == PENDING_OK
+	  )
+	  done = TRUE;
+	else
+	  done = (options & vopt_callout_fullpm) != 0
+	      && smtp_write_command(&sx, SCMD_FLUSH,
+			    "RCPT TO:<postmaster>\r\n") >= 0
+	      && smtp_read_response(&sx, sx.buffer,
+			    sizeof(sx.buffer), '2', callout);
+
+	/* Sort out the cache record */
+
+	new_domain_record.postmaster_stamp = time(NULL);
+
+	if (done)
+	  new_domain_record.postmaster_result = ccache_accept;
+	else if (errno == 0 && sx.buffer[0] == '5')
+	  {
+	  *failure_ptr = US"postmaster";
+	  setflag(addr, af_verify_pmfail);
+	  new_domain_record.postmaster_result = ccache_reject;
+	  }
+
+	addr->address = main_address;
+	}
+      }
+    /* For any failure of the main check, other than a negative response, we just
+    close the connection and carry on. We can identify a negative response by the
+    fact that errno is zero. For I/O errors it will be non-zero
+
+    Set up different error texts for logging and for sending back to the caller
+    as an SMTP response. Log in all cases, using a one-line format. For sender
+    callouts, give a full response to the caller, but for recipient callouts,
+    don't give the IP address because this may be an internal host whose identity
+    is not to be widely broadcast. */
+
+no_conn:
+    switch(errno)
+      {
+      case ETIMEDOUT:
+	HDEBUG(D_verify) debug_printf("SMTP timeout\n");
+	sx.send_quit = FALSE;
+	break;
+
+#ifdef SUPPORT_I18N
+      case ERRNO_UTF8_FWD:
+	{
+	extern int acl_where;	/* src/acl.c */
+	errno = 0;
+	addr->message = string_sprintf(
+	    "response to \"EHLO\" did not include SMTPUTF8");
+	addr->user_message = acl_where == ACL_WHERE_RCPT
+	  ? US"533 no support for internationalised mailbox name"
+	  : US"550 mailbox unavailable";
+	yield = FAIL;
+	done = TRUE;
+	}
+	break;
+#endif
+#if defined(SUPPORT_TLS) && defined(EXPERIMENTAL_REQUIRETLS)
+      case ERRNO_REQUIRETLS:
+        addr->user_message = US"530 5.7.4 REQUIRETLS support required";
+	yield = FAIL;
+	done = TRUE;
+	break;
+#endif
+      case ECONNREFUSED:
+	sx.send_quit = FALSE;
+	break;
+
+      case 0:
+	if (*sx.buffer == 0) Ustrcpy(sx.buffer, US"connection dropped");
+
+	/*XXX test here is ugly; seem to have a split of responsibility for
+	building this message.  Need to rationalise.  Where is it done
+	before here, and when not?
+	Not == 5xx resp to MAIL on main-verify
+	*/
+	if (!addr->message) addr->message =
+	  string_sprintf("response to \"%s\" was: %s",
+			  big_buffer, string_printing(sx.buffer));
+
+	addr->user_message = options & vopt_is_recipient
+	  ? string_sprintf("Callout verification failed:\n%s", sx.buffer)
+	  : string_sprintf("Called:   %s\nSent:     %s\nResponse: %s",
+	    host->address, big_buffer, sx.buffer);
+
+	/* Hard rejection ends the process */
+
+	if (sx.buffer[0] == '5')   /* Address rejected */
+	  {
+	  yield = FAIL;
+	  done = TRUE;
+	  }
+	break;
+      }
+
+    /* End the SMTP conversation and close the connection. */
+
+    /* Cutthrough - on a successful connect and recipient-verify with
+    use-sender and we are 1st rcpt and have no cutthrough conn so far
+    here is where we want to leave the conn open.  Ditto for a lazy-close
+    verify. */
+
+    if (cutthrough.delivery)
+      {
+      if (addr->transport->filter_command)
+        {
+        cutthrough.delivery= FALSE;
+        HDEBUG(D_acl|D_v) debug_printf("Cutthrough cancelled by presence of transport filter\n");
+        }
+#ifndef DISABLE_DKIM
+      if (ob->dkim.dkim_domain)
+        {
+        cutthrough.delivery= FALSE;
+        HDEBUG(D_acl|D_v) debug_printf("Cutthrough cancelled by presence of DKIM signing\n");
+        }
+#endif
+#ifdef EXPERIMENTAL_ARC
+      if (ob->arc_sign)
+        {
+        cutthrough.delivery= FALSE;
+        HDEBUG(D_acl|D_v) debug_printf("Cutthrough cancelled by presence of ARC signing\n");
+        }
+#endif
+      }
+
+    if (  (cutthrough.delivery || options & vopt_callout_hold)
+       && rcpt_count == 1
+       && done
+       && yield == OK
+       &&    (options & (vopt_callout_recipsender|vopt_callout_recippmaster|vopt_success_on_redirect))
+	   == vopt_callout_recipsender
+       && !random_local_part
+       && !pm_mailfrom
+       && cutthrough.cctx.sock < 0
+       && !sx.lmtp
+       )
+      {
+      address_item * parent, * caddr;
+
+      HDEBUG(D_acl|D_v) debug_printf_indent("holding verify callout open for %s\n",
+	cutthrough.delivery
+	? "cutthrough delivery" : "potential further verifies and delivery");
+
+      cutthrough.callout_hold_only = !cutthrough.delivery;
+      cutthrough.is_tls =	tls_out.active.sock >= 0;
+      /* We assume no buffer in use in the outblock */
+      cutthrough.cctx =		sx.cctx;
+      cutthrough.nrcpt =	1;
+      cutthrough.transport =	addr->transport->name;
+      cutthrough.interface =	interface;
+      cutthrough.snd_port =	sending_port;
+      cutthrough.peer_options =	smtp_peer_options;
+      cutthrough.host =		*host;
+	{
+	int oldpool = store_pool;
+	store_pool = POOL_PERM;
+	cutthrough.snd_ip = string_copy(sending_ip_address);
+	cutthrough.host.name = string_copy(host->name);
+	cutthrough.host.address = string_copy(host->address);
+	store_pool = oldpool;
+	}
+
+      /* Save the address_item and parent chain for later logging */
+      cutthrough.addr =		*addr;
+      cutthrough.addr.next =	NULL;
+      cutthrough.addr.host_used = &cutthrough.host;
+      for (caddr = &cutthrough.addr, parent = addr->parent;
+	   parent;
+	   caddr = caddr->parent, parent = parent->parent)
+        *(caddr->parent = store_get(sizeof(address_item))) = *parent;
+
+      ctctx.outblock.buffer = ctbuffer;
+      ctctx.outblock.buffersize = sizeof(ctbuffer);
+      ctctx.outblock.ptr = ctbuffer;
+      /* ctctx.outblock.cmd_count = 0; ctctx.outblock.authenticating = FALSE; */
+      ctctx.outblock.cctx = &cutthrough.cctx;
+      }
+    else
+      {
+      /* Ensure no cutthrough on multiple verifies that were incompatible */
+      if (options & vopt_callout_recipsender)
+        cancel_cutthrough_connection(TRUE, US"not usable for cutthrough");
+      if (sx.send_quit)
+	{
+	(void) smtp_write_command(&sx, SCMD_FLUSH, "QUIT\r\n");
+
+	/* Wait a short time for response, and discard it */
+	smtp_read_response(&sx, sx.buffer, sizeof(sx.buffer), '2', 1);
+	}
+
+      if (sx.cctx.sock >= 0)
+	{
+#ifdef SUPPORT_TLS
+	if (sx.cctx.tls_ctx)
+	  {
+	  tls_close(sx.cctx.tls_ctx, TLS_SHUTDOWN_NOWAIT);
+	  sx.cctx.tls_ctx = NULL;
+	  }
+#endif
+	HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP(close)>>\n");
+	(void)close(sx.cctx.sock);
+	sx.cctx.sock = -1;
+#ifndef DISABLE_EVENT
+	(void) event_raise(addr->transport->event_action, US"tcp:close", NULL);
+#endif
+	}
+      }
+
+    if (!done || yield != OK)
+      addr->message = string_sprintf("%s [%s] : %s", host->name, host->address,
+				    addr->message);
+    }    /* Loop through all hosts, while !done */
+  }
+
+/* If we get here with done == TRUE, a successful callout happened, and yield
+will be set OK or FAIL according to the response to the RCPT command.
+Otherwise, we looped through the hosts but couldn't complete the business.
+However, there may be domain-specific information to cache in both cases. */
+
+if (!(options & vopt_callout_no_cache))
+  cache_callout_write(&new_domain_record, addr->domain,
+    done, &new_address_record, address_key);
+
+/* Failure to connect to any host, or any response other than 2xx or 5xx is a
+temporary error. If there was only one host, and a response was received, leave
+it alone if supplying details. Otherwise, give a generic response. */
+
+if (!done)
+  {
+  uschar * dullmsg = string_sprintf("Could not complete %s verify callout",
+    options & vopt_is_recipient ? "recipient" : "sender");
+  yield = DEFER;
+
+  addr->message = host_list->next || !addr->message
+    ? dullmsg : string_sprintf("%s: %s", dullmsg, addr->message);
+
+  addr->user_message = smtp_return_error_details
+    ? string_sprintf("%s for <%s>.\n"
+      "The mail server(s) for the domain may be temporarily unreachable, or\n"
+      "they may be permanently unreachable from this server. In the latter case,\n%s",
+      dullmsg, addr->address,
+      options & vopt_is_recipient
+	? "the address will never be accepted."
+        : "you need to change the address or create an MX record for its domain\n"
+	  "if it is supposed to be generally accessible from the Internet.\n"
+	  "Talk to your mail administrator for details.")
+    : dullmsg;
+
+  /* Force a specific error code */
+
+  addr->basic_errno = ERRNO_CALLOUTDEFER;
+  }
+
+/* Come here from within the cache-reading code on fast-track exit. */
+
+END_CALLOUT:
+tls_modify_variables(&tls_in);
+return yield;
+}
+
+
+
+/* Called after recipient-acl to get a cutthrough connection open when
+   one was requested and a recipient-verify wasn't subsequently done.
+*/
+int
+open_cutthrough_connection(address_item * addr)
+{
+address_item addr2;
+int rc;
+
+/* Use a recipient-verify-callout to set up the cutthrough connection. */
+/* We must use a copy of the address for verification, because it might
+get rewritten. */
+
+addr2 = *addr;
+HDEBUG(D_acl) debug_printf_indent("----------- %s cutthrough setup ------------\n",
+  rcpt_count > 1 ? "more" : "start");
+rc = verify_address(&addr2, NULL,
+	vopt_is_recipient | vopt_callout_recipsender | vopt_callout_no_cache,
+	CUTTHROUGH_CMD_TIMEOUT, -1, -1,
+	NULL, NULL, NULL);
+addr->message = addr2.message;
+addr->user_message = addr2.user_message;
+HDEBUG(D_acl) debug_printf_indent("----------- end cutthrough setup ------------\n");
+return rc;
+}
+
+
+
+/* Send given number of bytes from the buffer */
+static BOOL
+cutthrough_send(int n)
+{
+if(cutthrough.cctx.sock < 0)
+  return TRUE;
+
+if(
+#ifdef SUPPORT_TLS
+   cutthrough.is_tls
+   ? tls_write(cutthrough.cctx.tls_ctx, ctctx.outblock.buffer, n, FALSE)
+   :
+#endif
+     send(cutthrough.cctx.sock, ctctx.outblock.buffer, n, 0) > 0
+  )
+{
+  transport_count += n;
+  ctctx.outblock.ptr= ctctx.outblock.buffer;
+  return TRUE;
+}
+
+HDEBUG(D_transport|D_acl) debug_printf_indent("cutthrough_send failed: %s\n", strerror(errno));
+return FALSE;
+}
+
+
+
+static BOOL
+_cutthrough_puts(uschar * cp, int n)
+{
+while(n--)
+ {
+ if(ctctx.outblock.ptr >= ctctx.outblock.buffer+ctctx.outblock.buffersize)
+   if(!cutthrough_send(ctctx.outblock.buffersize))
+     return FALSE;
+
+ *ctctx.outblock.ptr++ = *cp++;
+ }
+return TRUE;
+}
+
+/* Buffered output of counted data block.   Return boolean success */
+static BOOL
+cutthrough_puts(uschar * cp, int n)
+{
+if (cutthrough.cctx.sock < 0) return TRUE;
+if (_cutthrough_puts(cp, n))  return TRUE;
+cancel_cutthrough_connection(TRUE, US"transmit failed");
+return FALSE;
+}
+
+void
+cutthrough_data_puts(uschar * cp, int n)
+{
+if (cutthrough.delivery) (void) cutthrough_puts(cp, n);
+return;
+}
+
+
+static BOOL
+_cutthrough_flush_send(void)
+{
+int n = ctctx.outblock.ptr - ctctx.outblock.buffer;
+
+if(n>0)
+  if(!cutthrough_send(n))
+    return FALSE;
+return TRUE;
+}
+
+
+/* Send out any bufferred output.  Return boolean success. */
+BOOL
+cutthrough_flush_send(void)
+{
+if (_cutthrough_flush_send()) return TRUE;
+cancel_cutthrough_connection(TRUE, US"transmit failed");
+return FALSE;
+}
+
+
+static BOOL
+cutthrough_put_nl(void)
+{
+return cutthrough_puts(US"\r\n", 2);
+}
+
+
+void
+cutthrough_data_put_nl(void)
+{
+cutthrough_data_puts(US"\r\n", 2);
+}
+
+
+/* Get and check response from cutthrough target */
+static uschar
+cutthrough_response(client_conn_ctx * cctx, char expect, uschar ** copy, int timeout)
+{
+smtp_context sx = {0};
+uschar inbuffer[4096];
+uschar responsebuffer[4096];
+
+sx.inblock.buffer = inbuffer;
+sx.inblock.buffersize = sizeof(inbuffer);
+sx.inblock.ptr = inbuffer;
+sx.inblock.ptrend = inbuffer;
+sx.inblock.cctx = cctx;
+if(!smtp_read_response(&sx, responsebuffer, sizeof(responsebuffer), expect, timeout))
+  cancel_cutthrough_connection(TRUE, US"target timeout on read");
+
+if(copy)
+  {
+  uschar * cp;
+  *copy = cp = string_copy(responsebuffer);
+  /* Trim the trailing end of line */
+  cp += Ustrlen(responsebuffer);
+  if(cp > *copy  &&  cp[-1] == '\n') *--cp = '\0';
+  if(cp > *copy  &&  cp[-1] == '\r') *--cp = '\0';
+  }
+
+return responsebuffer[0];
+}
+
+
+/* Negotiate dataphase with the cutthrough target, returning success boolean */
+BOOL
+cutthrough_predata(void)
+{
+if(cutthrough.cctx.sock < 0 || cutthrough.callout_hold_only)
+  return FALSE;
+
+HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP>> DATA\n");
+cutthrough_puts(US"DATA\r\n", 6);
+cutthrough_flush_send();
+
+/* Assume nothing buffered.  If it was it gets ignored. */
+return cutthrough_response(&cutthrough.cctx, '3', NULL, CUTTHROUGH_DATA_TIMEOUT) == '3';
+}
+
+
+/* tctx arg only to match write_chunk() */
+static BOOL
+cutthrough_write_chunk(transport_ctx * tctx, uschar * s, int len)
+{
+uschar * s2;
+while(s && (s2 = Ustrchr(s, '\n')))
+ {
+ if(!cutthrough_puts(s, s2-s) || !cutthrough_put_nl())
+  return FALSE;
+ s = s2+1;
+ }
+return TRUE;
+}
+
+
+/* Buffered send of headers.  Return success boolean. */
+/* Expands newlines to wire format (CR,NL).           */
+/* Also sends header-terminating blank line.          */
+BOOL
+cutthrough_headers_send(void)
+{
+transport_ctx tctx;
+
+if(cutthrough.cctx.sock < 0 || cutthrough.callout_hold_only)
+  return FALSE;
+
+/* We share a routine with the mainline transport to handle header add/remove/rewrites,
+   but having a separate buffered-output function (for now)
+*/
+HDEBUG(D_acl) debug_printf_indent("----------- start cutthrough headers send -----------\n");
+
+tctx.u.fd = cutthrough.cctx.sock;
+tctx.tblock = cutthrough.addr.transport;
+tctx.addr = &cutthrough.addr;
+tctx.check_string = US".";
+tctx.escape_string = US"..";
+/*XXX check under spool_files_wireformat.  Might be irrelevant */
+tctx.options = topt_use_crlf;
+
+if (!transport_headers_send(&tctx, &cutthrough_write_chunk))
+  return FALSE;
+
+HDEBUG(D_acl) debug_printf_indent("----------- done cutthrough headers send ------------\n");
+return TRUE;
+}
+
+
+static void
+close_cutthrough_connection(const uschar * why)
+{
+int fd = cutthrough.cctx.sock;
+if(fd >= 0)
+  {
+  /* We could be sending this after a bunch of data, but that is ok as
+     the only way to cancel the transfer in dataphase is to drop the tcp
+     conn before the final dot.
+  */
+  client_conn_ctx tmp_ctx = cutthrough.cctx;
+  ctctx.outblock.ptr = ctbuffer;
+  HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP>> QUIT\n");
+  _cutthrough_puts(US"QUIT\r\n", 6);	/* avoid recursion */
+  _cutthrough_flush_send();
+  cutthrough.cctx.sock = -1;		/* avoid recursion via read timeout */
+  cutthrough.nrcpt = 0;			/* permit re-cutthrough on subsequent message */
+
+  /* Wait a short time for response, and discard it */
+  cutthrough_response(&tmp_ctx, '2', NULL, 1);
+
+#ifdef SUPPORT_TLS
+  if (cutthrough.is_tls)
+    {
+    tls_close(cutthrough.cctx.tls_ctx, TLS_SHUTDOWN_NOWAIT);
+    cutthrough.cctx.tls_ctx = NULL;
+    cutthrough.is_tls = FALSE;
+    }
+#endif
+  HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP(close)>>\n");
+  (void)close(fd);
+  HDEBUG(D_acl) debug_printf_indent("----------- cutthrough shutdown (%s) ------------\n", why);
+  }
+ctctx.outblock.ptr = ctbuffer;
+}
+
+void
+cancel_cutthrough_connection(BOOL close_noncutthrough_verifies, const uschar * why)
+{
+if (cutthrough.delivery || close_noncutthrough_verifies)
+  close_cutthrough_connection(why);
+cutthrough.delivery = cutthrough.callout_hold_only = FALSE;
+}
+
+
+void
+release_cutthrough_connection(const uschar * why)
+{
+if (cutthrough.cctx.sock < 0) return;
+HDEBUG(D_acl) debug_printf_indent("release cutthrough conn: %s\n", why);
+cutthrough.cctx.sock = -1;
+cutthrough.cctx.tls_ctx = NULL;
+cutthrough.delivery = cutthrough.callout_hold_only = FALSE;
+}
+
+
+
+
+/* Have senders final-dot.  Send one to cutthrough target, and grab the response.
+   Log an OK response as a transmission.
+   Close the connection.
+   Return smtp response-class digit.
+*/
+uschar *
+cutthrough_finaldot(void)
+{
+uschar res;
+address_item * addr;
+HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP>> .\n");
+
+/* Assume data finshed with new-line */
+if(  !cutthrough_puts(US".", 1)
+  || !cutthrough_put_nl()
+  || !cutthrough_flush_send()
+  )
+  return cutthrough.addr.message;
+
+res = cutthrough_response(&cutthrough.cctx, '2', &cutthrough.addr.message,
+	CUTTHROUGH_DATA_TIMEOUT);
+for (addr = &cutthrough.addr; addr; addr = addr->next)
+  {
+  addr->message = cutthrough.addr.message;
+  switch(res)
+    {
+    case '2':
+      delivery_log(LOG_MAIN, addr, (int)'>', NULL);
+      close_cutthrough_connection(US"delivered");
+      break;
+
+    case '4':
+      delivery_log(LOG_MAIN, addr, 0,
+	US"tmp-reject from cutthrough after DATA:");
+      break;
+
+    case '5':
+      delivery_log(LOG_MAIN|LOG_REJECT, addr, 0,
+	US"rejected after DATA:");
+      break;
+
+    default:
+      break;
+    }
+  }
+return cutthrough.addr.message;
+}
+
+
+
+/*************************************************
+*           Copy error to toplevel address       *
+*************************************************/
+
+/* This function is used when a verify fails or defers, to ensure that the
+failure or defer information is in the original toplevel address. This applies
+when an address is redirected to a single new address, and the failure or
+deferral happens to the child address.
+
+Arguments:
+  vaddr       the verify address item
+  addr        the final address item
+  yield       FAIL or DEFER
+
+Returns:      the value of YIELD
+*/
+
+static int
+copy_error(address_item *vaddr, address_item *addr, int yield)
+{
+if (addr != vaddr)
+  {
+  vaddr->message = addr->message;
+  vaddr->user_message = addr->user_message;
+  vaddr->basic_errno = addr->basic_errno;
+  vaddr->more_errno = addr->more_errno;
+  vaddr->prop.address_data = addr->prop.address_data;
+  copyflag(vaddr, addr, af_pass_message);
+  }
+return yield;
+}
+
+
+
+
+/**************************************************
+* printf that automatically handles TLS if needed *
+***************************************************/
+
+/* This function is used by verify_address() as a substitute for all fprintf()
+calls; a direct fprintf() will not produce output in a TLS SMTP session, such
+as a response to an EXPN command.  smtp_in.c makes smtp_printf available but
+that assumes that we always use the smtp_out FILE* when not using TLS or the
+ssl buffer when we are.  Instead we take a FILE* parameter and check to see if
+that is smtp_out; if so, smtp_printf() with TLS support, otherwise regular
+fprintf().
+
+Arguments:
+  f           the candidate FILE* to write to
+  format      format string
+  ...         optional arguments
+
+Returns:
+              nothing
+*/
+
+static void PRINTF_FUNCTION(2,3)
+respond_printf(FILE *f, const char *format, ...)
+{
+va_list ap;
+
+va_start(ap, format);
+if (smtp_out && (f == smtp_out))
+  smtp_vprintf(format, FALSE, ap);
+else
+  vfprintf(f, format, ap);
+va_end(ap);
+}
+
+
+
+/*************************************************
+*            Verify an email address             *
+*************************************************/
+
+/* This function is used both for verification (-bv and at other times) and
+address testing (-bt), which is indicated by address_test_mode being set.
+
+Arguments:
+  vaddr            contains the address to verify; the next field in this block
+                     must be NULL
+  f                if not NULL, write the result to this file
+  options          various option bits:
+                     vopt_fake_sender => this sender verify is not for the real
+                       sender (it was verify=sender=xxxx or an address from a
+                       header line) - rewriting must not change sender_address
+                     vopt_is_recipient => this is a recipient address, otherwise
+                       it's a sender address - this affects qualification and
+                       rewriting and messages from callouts
+                     vopt_qualify => qualify an unqualified address; else error
+                     vopt_expn => called from SMTP EXPN command
+                     vopt_success_on_redirect => when a new address is generated
+                       the verification instantly succeeds
+
+                     These ones are used by do_callout() -- the options variable
+                       is passed to it.
+
+                     vopt_callout_fullpm => if postmaster check, do full one
+                     vopt_callout_no_cache => don't use callout cache
+                     vopt_callout_random => do the "random" thing
+                     vopt_callout_recipsender => use real sender for recipient
+                     vopt_callout_recippmaster => use postmaster for recipient
+
+  callout          if > 0, specifies that callout is required, and gives timeout
+                     for individual commands
+  callout_overall  if > 0, gives overall timeout for the callout function;
+                   if < 0, a default is used (see do_callout())
+  callout_connect  the connection timeout for callouts
+  se_mailfrom      when callout is requested to verify a sender, use this
+                     in MAIL FROM; NULL => ""
+  pm_mailfrom      when callout is requested, if non-NULL, do the postmaster
+                     thing and use this as the sender address (may be "")
+
+  routed           if not NULL, set TRUE if routing succeeded, so we can
+                     distinguish between routing failed and callout failed
+
+Returns:           OK      address verified
+                   FAIL    address failed to verify
+                   DEFER   can't tell at present
+*/
+
+int
+verify_address(address_item * vaddr, FILE * fp, int options, int callout,
+  int callout_overall, int callout_connect, uschar * se_mailfrom,
+  uschar *pm_mailfrom, BOOL *routed)
+{
+BOOL allok = TRUE;
+BOOL full_info = fp ? debug_selector != 0 : FALSE;
+BOOL expn         = (options & vopt_expn) != 0;
+BOOL success_on_redirect = (options & vopt_success_on_redirect) != 0;
+int i;
+int yield = OK;
+int verify_type = expn? v_expn :
+   f.address_test_mode? v_none :
+          options & vopt_is_recipient? v_recipient : v_sender;
+address_item *addr_list;
+address_item *addr_new = NULL;
+address_item *addr_remote = NULL;
+address_item *addr_local = NULL;
+address_item *addr_succeed = NULL;
+uschar **failure_ptr = options & vopt_is_recipient
+  ? &recipient_verify_failure : &sender_verify_failure;
+uschar *ko_prefix, *cr;
+uschar *address = vaddr->address;
+uschar *save_sender;
+uschar null_sender[] = { 0 };             /* Ensure writeable memory */
+
+/* Clear, just in case */
+
+*failure_ptr = NULL;
+
+/* Set up a prefix and suffix for error message which allow us to use the same
+output statements both in EXPN mode (where an SMTP response is needed) and when
+debugging with an output file. */
+
+if (expn)
+  {
+  ko_prefix = US"553 ";
+  cr = US"\r";
+  }
+else ko_prefix = cr = US"";
+
+/* Add qualify domain if permitted; otherwise an unqualified address fails. */
+
+if (parse_find_at(address) == NULL)
+  {
+  if (!(options & vopt_qualify))
+    {
+    if (fp)
+      respond_printf(fp, "%sA domain is required for \"%s\"%s\n",
+        ko_prefix, address, cr);
+    *failure_ptr = US"qualify";
+    return FAIL;
+    }
+  address = rewrite_address_qualify(address, options & vopt_is_recipient);
+  }
+
+DEBUG(D_verify)
+  {
+  debug_printf(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n");
+  debug_printf("%s %s\n", f.address_test_mode? "Testing" : "Verifying", address);
+  }
+
+/* Rewrite and report on it. Clear the domain and local part caches - these
+may have been set by domains and local part tests during an ACL. */
+
+if (global_rewrite_rules)
+  {
+  uschar *old = address;
+  address = rewrite_address(address, options & vopt_is_recipient, FALSE,
+    global_rewrite_rules, rewrite_existflags);
+  if (address != old)
+    {
+    for (i = 0; i < (MAX_NAMED_LIST * 2)/32; i++) vaddr->localpart_cache[i] = 0;
+    for (i = 0; i < (MAX_NAMED_LIST * 2)/32; i++) vaddr->domain_cache[i] = 0;
+    if (fp && !expn) fprintf(fp, "Address rewritten as: %s\n", address);
+    }
+  }
+
+/* If this is the real sender address, we must update sender_address at
+this point, because it may be referred to in the routers. */
+
+if (!(options & (vopt_fake_sender|vopt_is_recipient)))
+  sender_address = address;
+
+/* If the address was rewritten to <> no verification can be done, and we have
+to return OK. This rewriting is permitted only for sender addresses; for other
+addresses, such rewriting fails. */
+
+if (!address[0]) return OK;
+
+/* Flip the legacy TLS-related variables over to the outbound set in case
+they're used in the context of a transport used by verification. Reset them
+at exit from this routine (so no returns allowed from here on). */
+
+tls_modify_variables(&tls_out);
+
+/* Save a copy of the sender address for re-instating if we change it to <>
+while verifying a sender address (a nice bit of self-reference there). */
+
+save_sender = sender_address;
+
+/* Observability variable for router/transport use */
+
+verify_mode = options & vopt_is_recipient ? US"R" : US"S";
+
+/* Update the address structure with the possibly qualified and rewritten
+address. Set it up as the starting address on the chain of new addresses. */
+
+vaddr->address = address;
+addr_new = vaddr;
+
+/* We need a loop, because an address can generate new addresses. We must also
+cope with generated pipes and files at the top level. (See also the code and
+comment in deliver.c.) However, it is usually the case that the router for
+user's .forward files has its verify flag turned off.
+
+If an address generates more than one child, the loop is used only when
+full_info is set, and this can only be set locally. Remote enquiries just get
+information about the top level address, not anything that it generated. */
+
+while (addr_new)
+  {
+  int rc;
+  address_item *addr = addr_new;
+
+  addr_new = addr->next;
+  addr->next = NULL;
+
+  DEBUG(D_verify)
+    {
+    debug_printf(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n");
+    debug_printf("Considering %s\n", addr->address);
+    }
+
+  /* Handle generated pipe, file or reply addresses. We don't get these
+  when handling EXPN, as it does only one level of expansion. */
+
+  if (testflag(addr, af_pfr))
+    {
+    allok = FALSE;
+    if (fp)
+      {
+      BOOL allow;
+
+      if (addr->address[0] == '>')
+        {
+        allow = testflag(addr, af_allow_reply);
+        fprintf(fp, "%s -> mail %s", addr->parent->address, addr->address + 1);
+        }
+      else
+        {
+        allow = addr->address[0] == '|'
+          ? testflag(addr, af_allow_pipe) : testflag(addr, af_allow_file);
+        fprintf(fp, "%s -> %s", addr->parent->address, addr->address);
+        }
+
+      if (addr->basic_errno == ERRNO_BADTRANSPORT)
+        fprintf(fp, "\n*** Error in setting up pipe, file, or autoreply:\n"
+          "%s\n", addr->message);
+      else if (allow)
+        fprintf(fp, "\n  transport = %s\n", addr->transport->name);
+      else
+        fprintf(fp, " *** forbidden ***\n");
+      }
+    continue;
+    }
+
+  /* Just in case some router parameter refers to it. */
+
+  return_path = addr->prop.errors_address
+    ? addr->prop.errors_address : sender_address;
+
+  /* Split the address into domain and local part, handling the %-hack if
+  necessary, and then route it. While routing a sender address, set
+  $sender_address to <> because that is what it will be if we were trying to
+  send a bounce to the sender. */
+
+  if (routed) *routed = FALSE;
+  if ((rc = deliver_split_address(addr)) == OK)
+    {
+    if (!(options & vopt_is_recipient)) sender_address = null_sender;
+    rc = route_address(addr, &addr_local, &addr_remote, &addr_new,
+      &addr_succeed, verify_type);
+    sender_address = save_sender;     /* Put back the real sender */
+    }
+
+  /* If routing an address succeeded, set the flag that remembers, for use when
+  an ACL cached a sender verify (in case a callout fails). Then if routing set
+  up a list of hosts or the transport has a host list, and the callout option
+  is set, and we aren't in a host checking run, do the callout verification,
+  and set another flag that notes that a callout happened. */
+
+  if (rc == OK)
+    {
+    if (routed) *routed = TRUE;
+    if (callout > 0)
+      {
+      transport_instance * tp;
+      host_item * host_list = addr->host_list;
+
+      /* Make up some data for use in the case where there is no remote
+      transport. */
+
+      transport_feedback tf = {
+        .interface =		NULL,                       /* interface (=> any) */
+        .port =			US"smtp",
+        .protocol =		US"smtp",
+        .hosts =		NULL,
+        .helo_data =		US"$smtp_active_hostname",
+        .hosts_override =	FALSE,
+        .hosts_randomize =	FALSE,
+        .gethostbyname =	FALSE,
+        .qualify_single =	TRUE,
+        .search_parents =	FALSE
+        };
+
+      /* If verification yielded a remote transport, we want to use that
+      transport's options, so as to mimic what would happen if we were really
+      sending a message to this address. */
+
+      if ((tp = addr->transport) && !tp->info->local)
+        {
+        (void)(tp->setup)(tp, addr, &tf, 0, 0, NULL);
+
+        /* If the transport has hosts and the router does not, or if the
+        transport is configured to override the router's hosts, we must build a
+        host list of the transport's hosts, and find the IP addresses */
+
+        if (tf.hosts && (!host_list || tf.hosts_override))
+          {
+          uschar *s;
+          const uschar *save_deliver_domain = deliver_domain;
+          uschar *save_deliver_localpart = deliver_localpart;
+
+          host_list = NULL;    /* Ignore the router's hosts */
+
+          deliver_domain = addr->domain;
+          deliver_localpart = addr->local_part;
+          s = expand_string(tf.hosts);
+          deliver_domain = save_deliver_domain;
+          deliver_localpart = save_deliver_localpart;
+
+          if (!s)
+            {
+            log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand list of hosts "
+              "\"%s\" in %s transport for callout: %s", tf.hosts,
+              tp->name, expand_string_message);
+            }
+          else
+            {
+            int flags;
+            host_item *host, *nexthost;
+            host_build_hostlist(&host_list, s, tf.hosts_randomize);
+
+            /* Just ignore failures to find a host address. If we don't manage
+            to find any addresses, the callout will defer. Note that more than
+            one address may be found for a single host, which will result in
+            additional host items being inserted into the chain. Hence we must
+            save the next host first. */
+
+            flags = HOST_FIND_BY_A | HOST_FIND_BY_AAAA;
+            if (tf.qualify_single) flags |= HOST_FIND_QUALIFY_SINGLE;
+            if (tf.search_parents) flags |= HOST_FIND_SEARCH_PARENTS;
+
+            for (host = host_list; host; host = nexthost)
+              {
+              nexthost = host->next;
+              if (tf.gethostbyname ||
+                  string_is_ip_address(host->name, NULL) != 0)
+                (void)host_find_byname(host, NULL, flags, NULL, TRUE);
+              else
+		{
+		const dnssec_domains * dsp = NULL;
+		if (Ustrcmp(tp->driver_name, "smtp") == 0)
+		  {
+		  smtp_transport_options_block * ob =
+		      (smtp_transport_options_block *) tp->options_block;
+		  dsp = &ob->dnssec;
+		  }
+
+                (void) host_find_bydns(host, NULL, flags, NULL, NULL, NULL,
+		  dsp, NULL, NULL);
+		}
+              }
+            }
+          }
+        }
+
+      /* Can only do a callout if we have at least one host! If the callout
+      fails, it will have set ${sender,recipient}_verify_failure. */
+
+      if (host_list)
+        {
+        HDEBUG(D_verify) debug_printf("Attempting full verification using callout\n");
+        if (host_checking && !f.host_checking_callout)
+          {
+          HDEBUG(D_verify)
+            debug_printf("... callout omitted by default when host testing\n"
+              "(Use -bhc if you want the callouts to happen.)\n");
+          }
+        else
+          {
+#ifdef SUPPORT_TLS
+	  deliver_set_expansions(addr);
+#endif
+          rc = do_callout(addr, host_list, &tf, callout, callout_overall,
+            callout_connect, options, se_mailfrom, pm_mailfrom);
+#ifdef SUPPORT_TLS
+	  deliver_set_expansions(NULL);
+#endif
+          }
+        }
+      else
+        {
+        HDEBUG(D_verify) debug_printf("Cannot do callout: neither router nor "
+          "transport provided a host list, or transport is not smtp\n");
+        }
+      }
+    }
+
+  /* Otherwise, any failure is a routing failure */
+
+  else *failure_ptr = US"route";
+
+  /* A router may return REROUTED if it has set up a child address as a result
+  of a change of domain name (typically from widening). In this case we always
+  want to continue to verify the new child. */
+
+  if (rc == REROUTED) continue;
+
+  /* Handle hard failures */
+
+  if (rc == FAIL)
+    {
+    allok = FALSE;
+    if (fp)
+      {
+      address_item *p = addr->parent;
+
+      respond_printf(fp, "%s%s %s", ko_prefix,
+        full_info ? addr->address : address,
+        f.address_test_mode ? "is undeliverable" : "failed to verify");
+      if (!expn && f.admin_user)
+        {
+        if (addr->basic_errno > 0)
+          respond_printf(fp, ": %s", strerror(addr->basic_errno));
+        if (addr->message)
+          respond_printf(fp, ": %s", addr->message);
+        }
+
+      /* Show parents iff doing full info */
+
+      if (full_info) while (p)
+        {
+        respond_printf(fp, "%s\n    <-- %s", cr, p->address);
+        p = p->parent;
+        }
+      respond_printf(fp, "%s\n", cr);
+      }
+    cancel_cutthrough_connection(TRUE, US"routing hard fail");
+
+    if (!full_info)
+      {
+      yield = copy_error(vaddr, addr, FAIL);
+      goto out;
+      }
+    yield = FAIL;
+    }
+
+  /* Soft failure */
+
+  else if (rc == DEFER)
+    {
+    allok = FALSE;
+    if (fp)
+      {
+      address_item *p = addr->parent;
+      respond_printf(fp, "%s%s cannot be resolved at this time", ko_prefix,
+        full_info? addr->address : address);
+      if (!expn && f.admin_user)
+        {
+        if (addr->basic_errno > 0)
+          respond_printf(fp, ": %s", strerror(addr->basic_errno));
+        if (addr->message)
+          respond_printf(fp, ": %s", addr->message);
+        else if (addr->basic_errno <= 0)
+          respond_printf(fp, ": unknown error");
+        }
+
+      /* Show parents iff doing full info */
+
+      if (full_info) while (p)
+        {
+        respond_printf(fp, "%s\n    <-- %s", cr, p->address);
+        p = p->parent;
+        }
+      respond_printf(fp, "%s\n", cr);
+      }
+    cancel_cutthrough_connection(TRUE, US"routing soft fail");
+
+    if (!full_info)
+      {
+      yield = copy_error(vaddr, addr, DEFER);
+      goto out;
+      }
+    if (yield == OK) yield = DEFER;
+    }
+
+  /* If we are handling EXPN, we do not want to continue to route beyond
+  the top level (whose address is in "address"). */
+
+  else if (expn)
+    {
+    uschar *ok_prefix = US"250-";
+
+    if (!addr_new)
+      if (!addr_local && !addr_remote)
+        respond_printf(fp, "250 mail to <%s> is discarded\r\n", address);
+      else
+        respond_printf(fp, "250 <%s>\r\n", address);
+
+    else do
+      {
+      address_item *addr2 = addr_new;
+      addr_new = addr2->next;
+      if (!addr_new) ok_prefix = US"250 ";
+      respond_printf(fp, "%s<%s>\r\n", ok_prefix, addr2->address);
+      } while (addr_new);
+    yield = OK;
+    goto out;
+    }
+
+  /* Successful routing other than EXPN. */
+
+  else
+    {
+    /* Handle successful routing when short info wanted. Otherwise continue for
+    other (generated) addresses. Short info is the operational case. Full info
+    can be requested only when debug_selector != 0 and a file is supplied.
+
+    There is a conflict between the use of aliasing as an alternate email
+    address, and as a sort of mailing list. If an alias turns the incoming
+    address into just one address (e.g. J.Caesar->jc44) you may well want to
+    carry on verifying the generated address to ensure it is valid when
+    checking incoming mail. If aliasing generates multiple addresses, you
+    probably don't want to do this. Exim therefore treats the generation of
+    just a single new address as a special case, and continues on to verify the
+    generated address. */
+
+    if (  !full_info			/* Stop if short info wanted AND */
+       && (  (  !addr_new		/* No new address OR */
+             || addr_new->next		/* More than one new address OR */
+	     || testflag(addr_new, af_pfr)	/* New address is pfr */
+	     )
+          ||				/* OR */
+             (  addr_new		/* At least one new address AND */
+             && success_on_redirect	/* success_on_redirect is set */
+	  )  )
+       )
+      {
+      if (fp) fprintf(fp, "%s %s\n",
+        address, f.address_test_mode ? "is deliverable" : "verified");
+
+      /* If we have carried on to verify a child address, we want the value
+      of $address_data to be that of the child */
+
+      vaddr->prop.address_data = addr->prop.address_data;
+
+      /* If stopped because more than one new address, cannot cutthrough */
+
+      if (addr_new && addr_new->next)
+	cancel_cutthrough_connection(TRUE, US"multiple addresses from routing");
+
+      yield = OK;
+      goto out;
+      }
+    }
+  }     /* Loop for generated addresses */
+
+/* Display the full results of the successful routing, including any generated
+addresses. Control gets here only when full_info is set, which requires fp not
+to be NULL, and this occurs only when a top-level verify is called with the
+debugging switch on.
+
+If there are no local and no remote addresses, and there were no pipes, files,
+or autoreplies, and there were no errors or deferments, the message is to be
+discarded, usually because of the use of :blackhole: in an alias file. */
+
+if (allok && !addr_local && !addr_remote)
+  {
+  fprintf(fp, "mail to %s is discarded\n", address);
+  goto out;
+  }
+
+for (addr_list = addr_local, i = 0; i < 2; addr_list = addr_remote, i++)
+  while (addr_list)
+    {
+    address_item *addr = addr_list;
+    address_item *p = addr->parent;
+    transport_instance * tp = addr->transport;
+
+    addr_list = addr->next;
+
+    fprintf(fp, "%s", CS addr->address);
+#ifdef EXPERIMENTAL_SRS
+    if(addr->prop.srs_sender)
+      fprintf(fp, "    [srs = %s]", addr->prop.srs_sender);
+#endif
+
+    /* If the address is a duplicate, show something about it. */
+
+    if (!testflag(addr, af_pfr))
+      {
+      tree_node *tnode;
+      if ((tnode = tree_search(tree_duplicates, addr->unique)))
+        fprintf(fp, "   [duplicate, would not be delivered]");
+      else tree_add_duplicate(addr->unique, addr);
+      }
+
+    /* Now show its parents */
+
+    for (p = addr->parent; p; p = p->parent)
+      fprintf(fp, "\n    <-- %s", p->address);
+    fprintf(fp, "\n  ");
+
+    /* Show router, and transport */
+
+    fprintf(fp, "router = %s, transport = %s\n",
+      addr->router->name, tp ? tp->name : US"unset");
+
+    /* Show any hosts that are set up by a router unless the transport
+    is going to override them; fiddle a bit to get a nice format. */
+
+    if (addr->host_list && tp && !tp->overrides_hosts)
+      {
+      host_item *h;
+      int maxlen = 0;
+      int maxaddlen = 0;
+      for (h = addr->host_list; h; h = h->next)
+        {				/* get max lengths of host names, addrs */
+        int len = Ustrlen(h->name);
+        if (len > maxlen) maxlen = len;
+        len = h->address ? Ustrlen(h->address) : 7;
+        if (len > maxaddlen) maxaddlen = len;
+        }
+      for (h = addr->host_list; h; h = h->next)
+	{
+	fprintf(fp, "  host %-*s ", maxlen, h->name);
+
+	if (h->address)
+	  fprintf(fp, "[%s%-*c", h->address, maxaddlen+1 - Ustrlen(h->address), ']');
+	else if (tp->info->local)
+	  fprintf(fp, " %-*s ", maxaddlen, "");  /* Omit [unknown] for local */
+	else
+	  fprintf(fp, "[%s%-*c", "unknown", maxaddlen+1 - 7, ']');
+
+        if (h->mx >= 0) fprintf(fp, " MX=%d", h->mx);
+        if (h->port != PORT_NONE) fprintf(fp, " port=%d", h->port);
+        if (f.running_in_test_harness  &&  h->dnssec == DS_YES) fputs(" AD", fp);
+        if (h->status == hstatus_unusable) fputs(" ** unusable **", fp);
+	fputc('\n', fp);
+        }
+      }
+    }
+
+/* Yield will be DEFER or FAIL if any one address has, only for full_info (which is
+the -bv or -bt case). */
+
+out:
+verify_mode = NULL;
+tls_modify_variables(&tls_in);
+
+return yield;
+}
+
+
+
+
+/*************************************************
+*      Check headers for syntax errors           *
+*************************************************/
+
+/* This function checks those header lines that contain addresses, and verifies
+that all the addresses therein are 5322-syntactially correct.
+
+Arguments:
+  msgptr     where to put an error message
+
+Returns:     OK
+             FAIL
+*/
+
+int
+verify_check_headers(uschar **msgptr)
+{
+header_line *h;
+uschar *colon, *s;
+int yield = OK;
+
+for (h = header_list; h && yield == OK; h = h->next)
+  {
+  if (h->type != htype_from &&
+      h->type != htype_reply_to &&
+      h->type != htype_sender &&
+      h->type != htype_to &&
+      h->type != htype_cc &&
+      h->type != htype_bcc)
+    continue;
+
+  colon = Ustrchr(h->text, ':');
+  s = colon + 1;
+  while (isspace(*s)) s++;
+
+  /* Loop for multiple addresses in the header, enabling group syntax. Note
+  that we have to reset this after the header has been scanned. */
+
+  f.parse_allow_group = TRUE;
+
+  while (*s)
+    {
+    uschar *ss = parse_find_address_end(s, FALSE);
+    uschar *recipient, *errmess;
+    int terminator = *ss;
+    int start, end, domain;
+
+    /* Temporarily terminate the string at this point, and extract the
+    operative address within, allowing group syntax. */
+
+    *ss = 0;
+    recipient = parse_extract_address(s,&errmess,&start,&end,&domain,FALSE);
+    *ss = terminator;
+
+    /* Permit an unqualified address only if the message is local, or if the
+    sending host is configured to be permitted to send them. */
+
+    if (recipient && !domain)
+      {
+      if (h->type == htype_from || h->type == htype_sender)
+        {
+        if (!f.allow_unqualified_sender) recipient = NULL;
+        }
+      else
+        {
+        if (!f.allow_unqualified_recipient) recipient = NULL;
+        }
+      if (recipient == NULL) errmess = US"unqualified address not permitted";
+      }
+
+    /* It's an error if no address could be extracted, except for the special
+    case of an empty address. */
+
+    if (!recipient && Ustrcmp(errmess, "empty address") != 0)
+      {
+      uschar *verb = US"is";
+      uschar *t = ss;
+      uschar *tt = colon;
+      int len;
+
+      /* Arrange not to include any white space at the end in the
+      error message or the header name. */
+
+      while (t > s && isspace(t[-1])) t--;
+      while (tt > h->text && isspace(tt[-1])) tt--;
+
+      /* Add the address that failed to the error message, since in a
+      header with very many addresses it is sometimes hard to spot
+      which one is at fault. However, limit the amount of address to
+      quote - cases have been seen where, for example, a missing double
+      quote in a humungous To: header creates an "address" that is longer
+      than string_sprintf can handle. */
+
+      len = t - s;
+      if (len > 1024)
+        {
+        len = 1024;
+        verb = US"begins";
+        }
+
+      /* deconst cast ok as we're passing a non-const to string_printing() */
+      *msgptr = US string_printing(
+        string_sprintf("%s: failing address in \"%.*s:\" header %s: %.*s",
+          errmess, (int)(tt - h->text), h->text, verb, len, s));
+
+      yield = FAIL;
+      break;          /* Out of address loop */
+      }
+
+    /* Advance to the next address */
+
+    s = ss + (terminator ? 1 : 0);
+    while (isspace(*s)) s++;
+    }   /* Next address */
+
+  f.parse_allow_group = FALSE;
+  f.parse_found_group = FALSE;
+  }     /* Next header unless yield has been set FALSE */
+
+return yield;
+}
+
+
+/*************************************************
+*      Check header names for 8-bit characters   *
+*************************************************/
+
+/* This function checks for invalid characters in header names. See
+RFC 5322, 2.2. and RFC 6532, 3.
+
+Arguments:
+  msgptr     where to put an error message
+
+Returns:     OK
+             FAIL
+*/
+
+int
+verify_check_header_names_ascii(uschar **msgptr)
+{
+header_line *h;
+uschar *colon, *s;
+
+for (h = header_list; h; h = h->next)
+  {
+  colon = Ustrchr(h->text, ':');
+  for(s = h->text; s < colon; s++)
+    if ((*s < 33) || (*s > 126))
+      {
+      *msgptr = string_sprintf("Invalid character in header \"%.*s\" found",
+			     colon - h->text, h->text);
+      return FAIL;
+      }
+  }
+return OK;
+}
+
+/*************************************************
+*          Check for blind recipients            *
+*************************************************/
+
+/* This function checks that every (envelope) recipient is mentioned in either
+the To: or Cc: header lines, thus detecting blind carbon copies.
+
+There are two ways of scanning that could be used: either scan the header lines
+and tick off the recipients, or scan the recipients and check the header lines.
+The original proposed patch did the former, but I have chosen to do the latter,
+because (a) it requires no memory and (b) will use fewer resources when there
+are many addresses in To: and/or Cc: and only one or two envelope recipients.
+
+Arguments:   none
+Returns:     OK    if there are no blind recipients
+             FAIL  if there is at least one blind recipient
+*/
+
+int
+verify_check_notblind(void)
+{
+int i;
+for (i = 0; i < recipients_count; i++)
+  {
+  header_line *h;
+  BOOL found = FALSE;
+  uschar *address = recipients_list[i].address;
+
+  for (h = header_list; !found && h != NULL; h = h->next)
+    {
+    uschar *colon, *s;
+
+    if (h->type != htype_to && h->type != htype_cc) continue;
+
+    colon = Ustrchr(h->text, ':');
+    s = colon + 1;
+    while (isspace(*s)) s++;
+
+    /* Loop for multiple addresses in the header, enabling group syntax. Note
+    that we have to reset this after the header has been scanned. */
+
+    f.parse_allow_group = TRUE;
+
+    while (*s != 0)
+      {
+      uschar *ss = parse_find_address_end(s, FALSE);
+      uschar *recipient,*errmess;
+      int terminator = *ss;
+      int start, end, domain;
+
+      /* Temporarily terminate the string at this point, and extract the
+      operative address within, allowing group syntax. */
+
+      *ss = 0;
+      recipient = parse_extract_address(s,&errmess,&start,&end,&domain,FALSE);
+      *ss = terminator;
+
+      /* If we found a valid recipient that has a domain, compare it with the
+      envelope recipient. Local parts are compared case-sensitively, domains
+      case-insensitively. By comparing from the start with length "domain", we
+      include the "@" at the end, which ensures that we are comparing the whole
+      local part of each address. */
+
+      if (recipient != NULL && domain != 0)
+        {
+        found = Ustrncmp(recipient, address, domain) == 0 &&
+                strcmpic(recipient + domain, address + domain) == 0;
+        if (found) break;
+        }
+
+      /* Advance to the next address */
+
+      s = ss + (terminator? 1:0);
+      while (isspace(*s)) s++;
+      }   /* Next address */
+
+    f.parse_allow_group = FALSE;
+    f.parse_found_group = FALSE;
+    }     /* Next header (if found is false) */
+
+  if (!found) return FAIL;
+  }       /* Next recipient */
+
+return OK;
+}
+
+
+
+/*************************************************
+*          Find if verified sender               *
+*************************************************/
+
+/* Usually, just a single address is verified as the sender of the message.
+However, Exim can be made to verify other addresses as well (often related in
+some way), and this is useful in some environments. There may therefore be a
+chain of such addresses that have previously been tested. This function finds
+whether a given address is on the chain.
+
+Arguments:   the address to be verified
+Returns:     pointer to an address item, or NULL
+*/
+
+address_item *
+verify_checked_sender(uschar *sender)
+{
+address_item *addr;
+for (addr = sender_verified_list; addr != NULL; addr = addr->next)
+  if (Ustrcmp(sender, addr->address) == 0) break;
+return addr;
+}
+
+
+
+
+
+/*************************************************
+*             Get valid header address           *
+*************************************************/
+
+/* Scan the originator headers of the message, looking for an address that
+verifies successfully. RFC 822 says:
+
+    o   The "Sender" field mailbox should be sent  notices  of
+        any  problems in transport or delivery of the original
+        messages.  If there is no  "Sender"  field,  then  the
+        "From" field mailbox should be used.
+
+    o   If the "Reply-To" field exists, then the reply  should
+        go to the addresses indicated in that field and not to
+        the address(es) indicated in the "From" field.
+
+So we check a Sender field if there is one, else a Reply_to field, else a From
+field. As some strange messages may have more than one of these fields,
+especially if they are resent- fields, check all of them if there is more than
+one.
+
+Arguments:
+  user_msgptr      points to where to put a user error message
+  log_msgptr       points to where to put a log error message
+  callout          timeout for callout check (passed to verify_address())
+  callout_overall  overall callout timeout (ditto)
+  callout_connect  connect callout timeout (ditto)
+  se_mailfrom      mailfrom for verify; NULL => ""
+  pm_mailfrom      sender for pm callout check (passed to verify_address())
+  options          callout options (passed to verify_address())
+  verrno           where to put the address basic_errno
+
+If log_msgptr is set to something without setting user_msgptr, the caller
+normally uses log_msgptr for both things.
+
+Returns:           result of the verification attempt: OK, FAIL, or DEFER;
+                   FAIL is given if no appropriate headers are found
+*/
+
+int
+verify_check_header_address(uschar **user_msgptr, uschar **log_msgptr,
+  int callout, int callout_overall, int callout_connect, uschar *se_mailfrom,
+  uschar *pm_mailfrom, int options, int *verrno)
+{
+static int header_types[] = { htype_sender, htype_reply_to, htype_from };
+BOOL done = FALSE;
+int yield = FAIL;
+int i;
+
+for (i = 0; i < 3 && !done; i++)
+  {
+  header_line *h;
+  for (h = header_list; h != NULL && !done; h = h->next)
+    {
+    int terminator, new_ok;
+    uschar *s, *ss, *endname;
+
+    if (h->type != header_types[i]) continue;
+    s = endname = Ustrchr(h->text, ':') + 1;
+
+    /* Scan the addresses in the header, enabling group syntax. Note that we
+    have to reset this after the header has been scanned. */
+
+    f.parse_allow_group = TRUE;
+
+    while (*s != 0)
+      {
+      address_item *vaddr;
+
+      while (isspace(*s) || *s == ',') s++;
+      if (*s == 0) break;        /* End of header */
+
+      ss = parse_find_address_end(s, FALSE);
+
+      /* The terminator is a comma or end of header, but there may be white
+      space preceding it (including newline for the last address). Move back
+      past any white space so we can check against any cached envelope sender
+      address verifications. */
+
+      while (isspace(ss[-1])) ss--;
+      terminator = *ss;
+      *ss = 0;
+
+      HDEBUG(D_verify) debug_printf("verifying %.*s header address %s\n",
+        (int)(endname - h->text), h->text, s);
+
+      /* See if we have already verified this address as an envelope sender,
+      and if so, use the previous answer. */
+
+      vaddr = verify_checked_sender(s);
+
+      if (vaddr != NULL &&                   /* Previously checked */
+           (callout <= 0 ||                  /* No callout needed; OR */
+            vaddr->special_action > 256))    /* Callout was done */
+        {
+        new_ok = vaddr->special_action & 255;
+        HDEBUG(D_verify) debug_printf("previously checked as envelope sender\n");
+        *ss = terminator;  /* Restore shortened string */
+        }
+
+      /* Otherwise we run the verification now. We must restore the shortened
+      string before running the verification, so the headers are correct, in
+      case there is any rewriting. */
+
+      else
+        {
+        int start, end, domain;
+        uschar *address = parse_extract_address(s, log_msgptr, &start, &end,
+          &domain, FALSE);
+
+        *ss = terminator;
+
+        /* If we found an empty address, just carry on with the next one, but
+        kill the message. */
+
+        if (address == NULL && Ustrcmp(*log_msgptr, "empty address") == 0)
+          {
+          *log_msgptr = NULL;
+          s = ss;
+          continue;
+          }
+
+        /* If verification failed because of a syntax error, fail this
+        function, and ensure that the failing address gets added to the error
+        message. */
+
+        if (address == NULL)
+          {
+          new_ok = FAIL;
+          while (ss > s && isspace(ss[-1])) ss--;
+          *log_msgptr = string_sprintf("syntax error in '%.*s' header when "
+            "scanning for sender: %s in \"%.*s\"",
+            (int)(endname - h->text), h->text, *log_msgptr, (int)(ss - s), s);
+          yield = FAIL;
+          done = TRUE;
+          break;
+          }
+
+        /* Else go ahead with the sender verification. But it isn't *the*
+        sender of the message, so set vopt_fake_sender to stop sender_address
+        being replaced after rewriting or qualification. */
+
+        else
+          {
+          vaddr = deliver_make_addr(address, FALSE);
+          new_ok = verify_address(vaddr, NULL, options | vopt_fake_sender,
+            callout, callout_overall, callout_connect, se_mailfrom,
+            pm_mailfrom, NULL);
+          }
+        }
+
+      /* We now have the result, either newly found, or cached. If we are
+      giving out error details, set a specific user error. This means that the
+      last of these will be returned to the user if all three fail. We do not
+      set a log message - the generic one below will be used. */
+
+      if (new_ok != OK)
+        {
+        *verrno = vaddr->basic_errno;
+        if (smtp_return_error_details)
+          *user_msgptr = string_sprintf("Rejected after DATA: "
+            "could not verify \"%.*s\" header address\n%s: %s",
+            (int)(endname - h->text), h->text, vaddr->address, vaddr->message);
+        }
+
+      /* Success or defer */
+
+      if (new_ok == OK)
+        {
+        yield = OK;
+        done = TRUE;
+        break;
+        }
+
+      if (new_ok == DEFER) yield = DEFER;
+
+      /* Move on to any more addresses in the header */
+
+      s = ss;
+      }     /* Next address */
+
+    f.parse_allow_group = FALSE;
+    f.parse_found_group = FALSE;
+    }       /* Next header, unless done */
+  }         /* Next header type unless done */
+
+if (yield == FAIL && *log_msgptr == NULL)
+  *log_msgptr = US"there is no valid sender in any header line";
+
+if (yield == DEFER && *log_msgptr == NULL)
+  *log_msgptr = US"all attempts to verify a sender in a header line deferred";
+
+return yield;
+}
+
+
+
+
+/*************************************************
+*            Get RFC 1413 identification         *
+*************************************************/
+
+/* Attempt to get an id from the sending machine via the RFC 1413 protocol. If
+the timeout is set to zero, then the query is not done. There may also be lists
+of hosts and nets which are exempt. To guard against malefactors sending
+non-printing characters which could, for example, disrupt a message's headers,
+make sure the string consists of printing characters only.
+
+Argument:
+  port    the port to connect to; usually this is IDENT_PORT (113), but when
+          running in the test harness with -bh a different value is used.
+
+Returns:  nothing
+
+Side effect: any received ident value is put in sender_ident (NULL otherwise)
+*/
+
+void
+verify_get_ident(int port)
+{
+client_conn_ctx ident_conn_ctx = {0};
+int host_af, qlen;
+int received_sender_port, received_interface_port, n;
+uschar *p;
+blob early_data;
+uschar buffer[2048];
+
+/* Default is no ident. Check whether we want to do an ident check for this
+host. */
+
+sender_ident = NULL;
+if (rfc1413_query_timeout <= 0 || verify_check_host(&rfc1413_hosts) != OK)
+  return;
+
+DEBUG(D_ident) debug_printf("doing ident callback\n");
+
+/* Set up a connection to the ident port of the remote host. Bind the local end
+to the incoming interface address. If the sender host address is an IPv6
+address, the incoming interface address will also be IPv6. */
+
+host_af = Ustrchr(sender_host_address, ':') == NULL ? AF_INET : AF_INET6;
+if ((ident_conn_ctx.sock = ip_socket(SOCK_STREAM, host_af)) < 0) return;
+
+if (ip_bind(ident_conn_ctx.sock, host_af, interface_address, 0) < 0)
+  {
+  DEBUG(D_ident) debug_printf("bind socket for ident failed: %s\n",
+    strerror(errno));
+  goto END_OFF;
+  }
+
+/* Construct and send the query. */
+
+qlen = snprintf(CS buffer, sizeof(buffer), "%d , %d\r\n",
+  sender_host_port, interface_port);
+early_data.data = buffer;
+early_data.len = qlen;
+
+/*XXX we trust that the query is idempotent */
+if (ip_connect(ident_conn_ctx.sock, host_af, sender_host_address, port,
+		rfc1413_query_timeout, &early_data) < 0)
+  {
+  if (errno == ETIMEDOUT && LOGGING(ident_timeout))
+    log_write(0, LOG_MAIN, "ident connection to %s timed out",
+      sender_host_address);
+  else
+    DEBUG(D_ident) debug_printf("ident connection to %s failed: %s\n",
+      sender_host_address, strerror(errno));
+  goto END_OFF;
+  }
+
+/* Read a response line. We put it into the rest of the buffer, using several
+recv() calls if necessary. */
+
+p = buffer + qlen;
+
+for (;;)
+  {
+  uschar *pp;
+  int count;
+  int size = sizeof(buffer) - (p - buffer);
+
+  if (size <= 0) goto END_OFF;   /* Buffer filled without seeing \n. */
+  count = ip_recv(&ident_conn_ctx, p, size, rfc1413_query_timeout);
+  if (count <= 0) goto END_OFF;  /* Read error or EOF */
+
+  /* Scan what we just read, to see if we have reached the terminating \r\n. Be
+  generous, and accept a plain \n terminator as well. The only illegal
+  character is 0. */
+
+  for (pp = p; pp < p + count; pp++)
+    {
+    if (*pp == 0) goto END_OFF;   /* Zero octet not allowed */
+    if (*pp == '\n')
+      {
+      if (pp[-1] == '\r') pp--;
+      *pp = 0;
+      goto GOT_DATA;             /* Break out of both loops */
+      }
+    }
+
+  /* Reached the end of the data without finding \n. Let the loop continue to
+  read some more, if there is room. */
+
+  p = pp;
+  }
+
+GOT_DATA:
+
+/* We have received a line of data. Check it carefully. It must start with the
+same two port numbers that we sent, followed by data as defined by the RFC. For
+example,
+
+  12345 , 25 : USERID : UNIX :root
+
+However, the amount of white space may be different to what we sent. In the
+"osname" field there may be several sub-fields, comma separated. The data we
+actually want to save follows the third colon. Some systems put leading spaces
+in it - we discard those. */
+
+if (sscanf(CS buffer + qlen, "%d , %d%n", &received_sender_port,
+      &received_interface_port, &n) != 2 ||
+    received_sender_port != sender_host_port ||
+    received_interface_port != interface_port)
+  goto END_OFF;
+
+p = buffer + qlen + n;
+while(isspace(*p)) p++;
+if (*p++ != ':') goto END_OFF;
+while(isspace(*p)) p++;
+if (Ustrncmp(p, "USERID", 6) != 0) goto END_OFF;
+p += 6;
+while(isspace(*p)) p++;
+if (*p++ != ':') goto END_OFF;
+while (*p != 0 && *p != ':') p++;
+if (*p++ == 0) goto END_OFF;
+while(isspace(*p)) p++;
+if (*p == 0) goto END_OFF;
+
+/* The rest of the line is the data we want. We turn it into printing
+characters when we save it, so that it cannot mess up the format of any logging
+or Received: lines into which it gets inserted. We keep a maximum of 127
+characters. The deconst cast is ok as we fed a nonconst to string_printing() */
+
+sender_ident = US string_printing(string_copyn(p, 127));
+DEBUG(D_ident) debug_printf("sender_ident = %s\n", sender_ident);
+
+END_OFF:
+(void)close(ident_conn_ctx.sock);
+return;
+}
+
+
+
+
+/*************************************************
+*      Match host to a single host-list item     *
+*************************************************/
+
+/* This function compares a host (name or address) against a single item
+from a host list. The host name gets looked up if it is needed and is not
+already known. The function is called from verify_check_this_host() via
+match_check_list(), which is why most of its arguments are in a single block.
+
+Arguments:
+  arg            the argument block (see below)
+  ss             the host-list item
+  valueptr       where to pass back looked up data, or NULL
+  error          for error message when returning ERROR
+
+The block contains:
+  host_name      (a) the host name, or
+                 (b) NULL, implying use sender_host_name and
+                       sender_host_aliases, looking them up if required, or
+                 (c) the empty string, meaning that only IP address matches
+                       are permitted
+  host_address   the host address
+  host_ipv4      the IPv4 address taken from an IPv6 one
+
+Returns:         OK      matched
+                 FAIL    did not match
+                 DEFER   lookup deferred
+                 ERROR   (a) failed to find the host name or IP address, or
+                         (b) unknown lookup type specified, or
+                         (c) host name encountered when only IP addresses are
+                               being matched
+*/
+
+int
+check_host(void *arg, const uschar *ss, const uschar **valueptr, uschar **error)
+{
+check_host_block *cb = (check_host_block *)arg;
+int mlen = -1;
+int maskoffset;
+BOOL iplookup = FALSE;
+BOOL isquery = FALSE;
+BOOL isiponly = cb->host_name != NULL && cb->host_name[0] == 0;
+const uschar *t;
+uschar *semicolon;
+uschar **aliases;
+
+/* Optimize for the special case when the pattern is "*". */
+
+if (*ss == '*' && ss[1] == 0) return OK;
+
+/* If the pattern is empty, it matches only in the case when there is no host -
+this can occur in ACL checking for SMTP input using the -bs option. In this
+situation, the host address is the empty string. */
+
+if (cb->host_address[0] == 0) return (*ss == 0)? OK : FAIL;
+if (*ss == 0) return FAIL;
+
+/* If the pattern is precisely "@" then match against the primary host name,
+provided that host name matching is permitted; if it's "@[]" match against the
+local host's IP addresses. */
+
+if (*ss == '@')
+  {
+  if (ss[1] == 0)
+    {
+    if (isiponly) return ERROR;
+    ss = primary_hostname;
+    }
+  else if (Ustrcmp(ss, "@[]") == 0)
+    {
+    ip_address_item *ip;
+    for (ip = host_find_interfaces(); ip != NULL; ip = ip->next)
+      if (Ustrcmp(ip->address, cb->host_address) == 0) return OK;
+    return FAIL;
+    }
+  }
+
+/* If the pattern is an IP address, optionally followed by a bitmask count, do
+a (possibly masked) comparison with the current IP address. */
+
+if (string_is_ip_address(ss, &maskoffset) != 0)
+  return (host_is_in_net(cb->host_address, ss, maskoffset)? OK : FAIL);
+
+/* The pattern is not an IP address. A common error that people make is to omit
+one component of an IPv4 address, either by accident, or believing that, for
+example, 1.2.3/24 is the same as 1.2.3.0/24, or 1.2.3 is the same as 1.2.3.0,
+which it isn't. (Those applications that do accept 1.2.3 as an IP address
+interpret it as 1.2.0.3 because the final component becomes 16-bit - this is an
+ancient specification.) To aid in debugging these cases, we give a specific
+error if the pattern contains only digits and dots or contains a slash preceded
+only by digits and dots (a slash at the start indicates a file name and of
+course slashes may be present in lookups, but not preceded only by digits and
+dots). */
+
+for (t = ss; isdigit(*t) || *t == '.'; t++);
+if (*t == 0 || (*t == '/' && t != ss))
+  {
+  *error = US"malformed IPv4 address or address mask";
+  return ERROR;
+  }
+
+/* See if there is a semicolon in the pattern */
+
+semicolon = Ustrchr(ss, ';');
+
+/* If we are doing an IP address only match, then all lookups must be IP
+address lookups, even if there is no "net-". */
+
+if (isiponly)
+  {
+  iplookup = semicolon != NULL;
+  }
+
+/* Otherwise, if the item is of the form net[n]-lookup;<file|query> then it is
+a lookup on a masked IP network, in textual form. We obey this code even if we
+have already set iplookup, so as to skip over the "net-" prefix and to set the
+mask length. The net- stuff really only applies to single-key lookups where the
+key is implicit. For query-style lookups the key is specified in the query.
+From release 4.30, the use of net- for query style is no longer needed, but we
+retain it for backward compatibility. */
+
+if (Ustrncmp(ss, "net", 3) == 0 && semicolon != NULL)
+  {
+  mlen = 0;
+  for (t = ss + 3; isdigit(*t); t++) mlen = mlen * 10 + *t - '0';
+  if (mlen == 0 && t == ss+3) mlen = -1;  /* No mask supplied */
+  iplookup = (*t++ == '-');
+  }
+else t = ss;
+
+/* Do the IP address lookup if that is indeed what we have */
+
+if (iplookup)
+  {
+  int insize;
+  int search_type;
+  int incoming[4];
+  void *handle;
+  uschar *filename, *key, *result;
+  uschar buffer[64];
+
+  /* Find the search type */
+
+  search_type = search_findtype(t, semicolon - t);
+
+  if (search_type < 0) log_write(0, LOG_MAIN|LOG_PANIC_DIE, "%s",
+    search_error_message);
+
+  /* Adjust parameters for the type of lookup. For a query-style lookup, there
+  is no file name, and the "key" is just the query. For query-style with a file
+  name, we have to fish the file off the start of the query. For a single-key
+  lookup, the key is the current IP address, masked appropriately, and
+  reconverted to text form, with the mask appended. For IPv6 addresses, specify
+  dot separators instead of colons, except when the lookup type is "iplsearch".
+  */
+
+  if (mac_islookup(search_type, lookup_absfilequery))
+    {
+    filename = semicolon + 1;
+    key = filename;
+    while (*key != 0 && !isspace(*key)) key++;
+    filename = string_copyn(filename, key - filename);
+    while (isspace(*key)) key++;
+    }
+  else if (mac_islookup(search_type, lookup_querystyle))
+    {
+    filename = NULL;
+    key = semicolon + 1;
+    }
+  else   /* Single-key style */
+    {
+    int sep = (Ustrcmp(lookup_list[search_type]->name, "iplsearch") == 0)?
+      ':' : '.';
+    insize = host_aton(cb->host_address, incoming);
+    host_mask(insize, incoming, mlen);
+    (void)host_nmtoa(insize, incoming, mlen, buffer, sep);
+    key = buffer;
+    filename = semicolon + 1;
+    }
+
+  /* Now do the actual lookup; note that there is no search_close() because
+  of the caching arrangements. */
+
+  if (!(handle = search_open(filename, search_type, 0, NULL, NULL)))
+    log_write(0, LOG_MAIN|LOG_PANIC_DIE, "%s", search_error_message);
+
+  result = search_find(handle, filename, key, -1, NULL, 0, 0, NULL);
+  if (valueptr) *valueptr = result;
+  return result ? OK : f.search_find_defer ? DEFER: FAIL;
+  }
+
+/* The pattern is not an IP address or network reference of any kind. That is,
+it is a host name pattern. If this is an IP only match, there's an error in the
+host list. */
+
+if (isiponly)
+  {
+  *error = US"cannot match host name in match_ip list";
+  return ERROR;
+  }
+
+/* Check the characters of the pattern to see if they comprise only letters,
+digits, full stops, and hyphens (the constituents of domain names). Allow
+underscores, as they are all too commonly found. Sigh. Also, if
+allow_utf8_domains is set, allow top-bit characters. */
+
+for (t = ss; *t != 0; t++)
+  if (!isalnum(*t) && *t != '.' && *t != '-' && *t != '_' &&
+      (!allow_utf8_domains || *t < 128)) break;
+
+/* If the pattern is a complete domain name, with no fancy characters, look up
+its IP address and match against that. Note that a multi-homed host will add
+items to the chain. */
+
+if (*t == 0)
+  {
+  int rc;
+  host_item h;
+  h.next = NULL;
+  h.name = ss;
+  h.address = NULL;
+  h.mx = MX_NONE;
+
+  /* Using byname rather than bydns here means we cannot determine dnssec
+  status.  On the other hand it is unclear how that could be either
+  propagated up or enforced. */
+
+  rc = host_find_byname(&h, NULL, HOST_FIND_QUALIFY_SINGLE, NULL, FALSE);
+  if (rc == HOST_FOUND || rc == HOST_FOUND_LOCAL)
+    {
+    host_item *hh;
+    for (hh = &h; hh != NULL; hh = hh->next)
+      {
+      if (host_is_in_net(hh->address, cb->host_address, 0)) return OK;
+      }
+    return FAIL;
+    }
+  if (rc == HOST_FIND_AGAIN) return DEFER;
+  *error = string_sprintf("failed to find IP address for %s", ss);
+  return ERROR;
+  }
+
+/* Almost all subsequent comparisons require the host name, and can be done
+using the general string matching function. When this function is called for
+outgoing hosts, the name is always given explicitly. If it is NULL, it means we
+must use sender_host_name and its aliases, looking them up if necessary. */
+
+if (cb->host_name != NULL)   /* Explicit host name given */
+  return match_check_string(cb->host_name, ss, -1, TRUE, TRUE, TRUE,
+    valueptr);
+
+/* Host name not given; in principle we need the sender host name and its
+aliases. However, for query-style lookups, we do not need the name if the
+query does not contain $sender_host_name. From release 4.23, a reference to
+$sender_host_name causes it to be looked up, so we don't need to do the lookup
+on spec. */
+
+if ((semicolon = Ustrchr(ss, ';')) != NULL)
+  {
+  const uschar *affix;
+  int partial, affixlen, starflags, id;
+
+  *semicolon = 0;
+  id = search_findtype_partial(ss, &partial, &affix, &affixlen, &starflags);
+  *semicolon=';';
+
+  if (id < 0)                           /* Unknown lookup type */
+    {
+    log_write(0, LOG_MAIN|LOG_PANIC, "%s in host list item \"%s\"",
+      search_error_message, ss);
+    return DEFER;
+    }
+  isquery = mac_islookup(id, lookup_querystyle|lookup_absfilequery);
+  }
+
+if (isquery)
+  {
+  switch(match_check_string(US"", ss, -1, TRUE, TRUE, TRUE, valueptr))
+    {
+    case OK:    return OK;
+    case DEFER: return DEFER;
+    default:    return FAIL;
+    }
+  }
+
+/* Not a query-style lookup; must ensure the host name is present, and then we
+do a check on the name and all its aliases. */
+
+if (!sender_host_name)
+  {
+  HDEBUG(D_host_lookup)
+    debug_printf("sender host name required, to match against %s\n", ss);
+  if (host_lookup_failed || host_name_lookup() != OK)
+    {
+    *error = string_sprintf("failed to find host name for %s",
+      sender_host_address);;
+    return ERROR;
+    }
+  host_build_sender_fullhost();
+  }
+
+/* Match on the sender host name, using the general matching function */
+
+switch(match_check_string(sender_host_name, ss, -1, TRUE, TRUE, TRUE, valueptr))
+  {
+  case OK:    return OK;
+  case DEFER: return DEFER;
+  }
+
+/* If there are aliases, try matching on them. */
+
+aliases = sender_host_aliases;
+while (*aliases)
+  switch(match_check_string(*aliases++, ss, -1, TRUE, TRUE, TRUE, valueptr))
+    {
+    case OK:    return OK;
+    case DEFER: return DEFER;
+    }
+return FAIL;
+}
+
+
+
+
+/*************************************************
+*    Check a specific host matches a host list   *
+*************************************************/
+
+/* This function is passed a host list containing items in a number of
+different formats and the identity of a host. Its job is to determine whether
+the given host is in the set of hosts defined by the list. The host name is
+passed as a pointer so that it can be looked up if needed and not already
+known. This is commonly the case when called from verify_check_host() to check
+an incoming connection. When called from elsewhere the host name should usually
+be set.
+
+This function is now just a front end to match_check_list(), which runs common
+code for scanning a list. We pass it the check_host() function to perform a
+single test.
+
+Arguments:
+  listptr              pointer to the host list
+  cache_bits           pointer to cache for named lists, or NULL
+  host_name            the host name or NULL, implying use sender_host_name and
+                         sender_host_aliases, looking them up if required
+  host_address         the IP address
+  valueptr             if not NULL, data from a lookup is passed back here
+
+Returns:    OK    if the host is in the defined set
+            FAIL  if the host is not in the defined set,
+            DEFER if a data lookup deferred (not a host lookup)
+
+If the host name was needed in order to make a comparison, and could not be
+determined from the IP address, the result is FAIL unless the item
+"+allow_unknown" was met earlier in the list, in which case OK is returned. */
+
+int
+verify_check_this_host(const uschar **listptr, unsigned int *cache_bits,
+  const uschar *host_name, const uschar *host_address, const uschar **valueptr)
+{
+int rc;
+unsigned int *local_cache_bits = cache_bits;
+const uschar *save_host_address = deliver_host_address;
+check_host_block cb = { .host_name = host_name, .host_address = host_address };
+
+if (valueptr) *valueptr = NULL;
+
+/* If the host address starts off ::ffff: it is an IPv6 address in
+IPv4-compatible mode. Find the IPv4 part for checking against IPv4
+addresses. */
+
+cb.host_ipv4 = Ustrncmp(host_address, "::ffff:", 7) == 0
+  ? host_address + 7 : host_address;
+
+/* During the running of the check, put the IP address into $host_address. In
+the case of calls from the smtp transport, it will already be there. However,
+in other calls (e.g. when testing ignore_target_hosts), it won't. Just to be on
+the safe side, any existing setting is preserved, though as I write this
+(November 2004) I can't see any cases where it is actually needed. */
+
+deliver_host_address = host_address;
+rc = match_check_list(
+       listptr,                                /* the list */
+       0,                                      /* separator character */
+       &hostlist_anchor,                       /* anchor pointer */
+       &local_cache_bits,                      /* cache pointer */
+       check_host,                             /* function for testing */
+       &cb,                                    /* argument for function */
+       MCL_HOST,                               /* type of check */
+       (host_address == sender_host_address)?
+         US"host" : host_address,              /* text for debugging */
+       valueptr);                              /* where to pass back data */
+deliver_host_address = save_host_address;
+return rc;
+}
+
+
+
+
+/*************************************************
+*      Check the given host item matches a list  *
+*************************************************/
+int
+verify_check_given_host(const uschar **listptr, const host_item *host)
+{
+return verify_check_this_host(listptr, NULL, host->name, host->address, NULL);
+}
+
+/*************************************************
+*      Check the remote host matches a list      *
+*************************************************/
+
+/* This is a front end to verify_check_this_host(), created because checking
+the remote host is a common occurrence. With luck, a good compiler will spot
+the tail recursion and optimize it. If there's no host address, this is
+command-line SMTP input - check against an empty string for the address.
+
+Arguments:
+  listptr              pointer to the host list
+
+Returns:               the yield of verify_check_this_host(),
+                       i.e. OK, FAIL, or DEFER
+*/
+
+int
+verify_check_host(uschar **listptr)
+{
+return verify_check_this_host(CUSS listptr, sender_host_cache, NULL,
+  (sender_host_address == NULL)? US"" : sender_host_address, NULL);
+}
+
+
+
+
+
+/*************************************************
+*              Invert an IP address              *
+*************************************************/
+
+/* Originally just used for DNS xBL lists, now also used for the
+reverse_ip expansion operator.
+
+Arguments:
+  buffer         where to put the answer
+  address        the address to invert
+*/
+
+void
+invert_address(uschar *buffer, uschar *address)
+{
+int bin[4];
+uschar *bptr = buffer;
+
+/* If this is an IPv4 address mapped into IPv6 format, adjust the pointer
+to the IPv4 part only. */
+
+if (Ustrncmp(address, "::ffff:", 7) == 0) address += 7;
+
+/* Handle IPv4 address: when HAVE_IPV6 is false, the result of host_aton() is
+always 1. */
+
+if (host_aton(address, bin) == 1)
+  {
+  int i;
+  int x = bin[0];
+  for (i = 0; i < 4; i++)
+    {
+    sprintf(CS bptr, "%d.", x & 255);
+    while (*bptr) bptr++;
+    x >>= 8;
+    }
+  }
+
+/* Handle IPv6 address. Actually, as far as I know, there are no IPv6 addresses
+in any DNS black lists, and the format in which they will be looked up is
+unknown. This is just a guess. */
+
+#if HAVE_IPV6
+else
+  {
+  int i, j;
+  for (j = 3; j >= 0; j--)
+    {
+    int x = bin[j];
+    for (i = 0; i < 8; i++)
+      {
+      sprintf(CS bptr, "%x.", x & 15);
+      while (*bptr) bptr++;
+      x >>= 4;
+      }
+    }
+  }
+#endif
+
+/* Remove trailing period -- this is needed so that both arbitrary
+dnsbl keydomains and inverted addresses may be combined with the
+same format string, "%s.%s" */
+
+*(--bptr) = 0;
+}
+
+
+
+/*************************************************
+*          Perform a single dnsbl lookup         *
+*************************************************/
+
+/* This function is called from verify_check_dnsbl() below. It is also called
+recursively from within itself when domain and domain_txt are different
+pointers, in order to get the TXT record from the alternate domain.
+
+Arguments:
+  domain         the outer dnsbl domain
+  domain_txt     alternate domain to lookup TXT record on success; when the
+                   same domain is to be used, domain_txt == domain (that is,
+                   the pointers must be identical, not just the text)
+  keydomain      the current keydomain (for debug message)
+  prepend        subdomain to lookup (like keydomain, but
+                   reversed if IP address)
+  iplist         the list of matching IP addresses, or NULL for "any"
+  bitmask        true if bitmask matching is wanted
+  match_type     condition for 'succeed' result
+                   0 => Any RR in iplist     (=)
+                   1 => No RR in iplist      (!=)
+                   2 => All RRs in iplist    (==)
+                   3 => Some RRs not in iplist (!==)
+                   the two bits are defined as MT_NOT and MT_ALL
+  defer_return   what to return for a defer
+
+Returns:         OK if lookup succeeded
+                 FAIL if not
+*/
+
+static int
+one_check_dnsbl(uschar *domain, uschar *domain_txt, uschar *keydomain,
+  uschar *prepend, uschar *iplist, BOOL bitmask, int match_type,
+  int defer_return)
+{
+dns_answer dnsa;
+dns_scan dnss;
+tree_node *t;
+dnsbl_cache_block *cb;
+int old_pool = store_pool;
+uschar query[256];         /* DNS domain max length */
+
+/* Construct the specific query domainname */
+
+if (!string_format(query, sizeof(query), "%s.%s", prepend, domain))
+  {
+  log_write(0, LOG_MAIN|LOG_PANIC, "dnslist query is too long "
+    "(ignored): %s...", query);
+  return FAIL;
+  }
+
+/* Look for this query in the cache. */
+
+if (  (t = tree_search(dnsbl_cache, query))
+   && (cb = t->data.ptr)->expiry > time(NULL)
+   )
+
+/* Previous lookup was cached */
+
+  {
+  HDEBUG(D_dnsbl) debug_printf("using result of previous DNS lookup\n");
+  }
+
+/* If not cached from a previous lookup, we must do a DNS lookup, and
+cache the result in permanent memory. */
+
+else
+  {
+  uint ttl = 3600;
+
+  store_pool = POOL_PERM;
+
+  if (t)
+    {
+    HDEBUG(D_dnsbl) debug_printf("cached data found but past valid time; ");
+    }
+
+  else
+    {	/* Set up a tree entry to cache the lookup */
+    t = store_get(sizeof(tree_node) + Ustrlen(query));
+    Ustrcpy(t->name, query);
+    t->data.ptr = cb = store_get(sizeof(dnsbl_cache_block));
+    (void)tree_insertnode(&dnsbl_cache, t);
+    }
+
+  /* Do the DNS lookup . */
+
+  HDEBUG(D_dnsbl) debug_printf("new DNS lookup for %s\n", query);
+  cb->rc = dns_basic_lookup(&dnsa, query, T_A);
+  cb->text_set = FALSE;
+  cb->text = NULL;
+  cb->rhs = NULL;
+
+  /* If the lookup succeeded, cache the RHS address. The code allows for
+  more than one address - this was for complete generality and the possible
+  use of A6 records. However, A6 records are no longer supported. Leave the code
+  here, just in case.
+
+  Quite apart from one A6 RR generating multiple addresses, there are DNS
+  lists that return more than one A record, so we must handle multiple
+  addresses generated in that way as well.
+
+  Mark the cache entry with the "now" plus the minimum of the address TTLs,
+  or some suitably far-future time if none were found. */
+
+  if (cb->rc == DNS_SUCCEED)
+    {
+    dns_record *rr;
+    dns_address **addrp = &(cb->rhs);
+    for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
+         rr;
+         rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
+      if (rr->type == T_A)
+        {
+        dns_address *da = dns_address_from_rr(&dnsa, rr);
+        if (da)
+          {
+          *addrp = da;
+          while (da->next) da = da->next;
+          addrp = &da->next;
+	  if (ttl > rr->ttl) ttl = rr->ttl;
+          }
+        }
+
+    /* If we didn't find any A records, change the return code. This can
+    happen when there is a CNAME record but there are no A records for what
+    it points to. */
+
+    if (!cb->rhs) cb->rc = DNS_NODATA;
+    }
+
+  cb->expiry = time(NULL)+ttl;
+  store_pool = old_pool;
+  }
+
+/* We now have the result of the DNS lookup, either newly done, or cached
+from a previous call. If the lookup succeeded, check against the address
+list if there is one. This may be a positive equality list (introduced by
+"="), a negative equality list (introduced by "!="), a positive bitmask
+list (introduced by "&"), or a negative bitmask list (introduced by "!&").*/
+
+if (cb->rc == DNS_SUCCEED)
+  {
+  dns_address *da = NULL;
+  uschar *addlist = cb->rhs->address;
+
+  /* For A and AAAA records, there may be multiple addresses from multiple
+  records. For A6 records (currently not expected to be used) there may be
+  multiple addresses from a single record. */
+
+  for (da = cb->rhs->next; da; da = da->next)
+    addlist = string_sprintf("%s, %s", addlist, da->address);
+
+  HDEBUG(D_dnsbl) debug_printf("DNS lookup for %s succeeded (yielding %s)\n",
+    query, addlist);
+
+  /* Address list check; this can be either for equality, or via a bitmask.
+  In the latter case, all the bits must match. */
+
+  if (iplist)
+    {
+    for (da = cb->rhs; da; da = da->next)
+      {
+      int ipsep = ',';
+      uschar ip[46];
+      const uschar *ptr = iplist;
+      uschar *res;
+
+      /* Handle exact matching */
+
+      if (!bitmask)
+	{
+        while ((res = string_nextinlist(&ptr, &ipsep, ip, sizeof(ip))))
+          if (Ustrcmp(CS da->address, ip) == 0)
+	    break;
+	}
+
+      /* Handle bitmask matching */
+
+      else
+        {
+        int address[4];
+        int mask = 0;
+
+        /* At present, all known DNS blocking lists use A records, with
+        IPv4 addresses on the RHS encoding the information they return. I
+        wonder if this will linger on as the last vestige of IPv4 when IPv6
+        is ubiquitous? Anyway, for now we use paranoia code to completely
+        ignore IPv6 addresses. The default mask is 0, which always matches.
+        We change this only for IPv4 addresses in the list. */
+
+        if (host_aton(da->address, address) == 1) mask = address[0];
+
+        /* Scan the returned addresses, skipping any that are IPv6 */
+
+        while ((res = string_nextinlist(&ptr, &ipsep, ip, sizeof(ip))))
+          {
+          if (host_aton(ip, address) != 1) continue;
+          if ((address[0] & mask) == address[0]) break;
+          }
+        }
+
+      /* If either
+
+         (a) An IP address in an any ('=') list matched, or
+         (b) No IP address in an all ('==') list matched
+
+      then we're done searching. */
+
+      if (((match_type & MT_ALL) != 0) == (res == NULL)) break;
+      }
+
+    /* If da == NULL, either
+
+       (a) No IP address in an any ('=') list matched, or
+       (b) An IP address in an all ('==') list didn't match
+
+    so behave as if the DNSBL lookup had not succeeded, i.e. the host is not on
+    the list. */
+
+    if ((match_type == MT_NOT || match_type == MT_ALL) != (da == NULL))
+      {
+      HDEBUG(D_dnsbl)
+        {
+        uschar *res = NULL;
+        switch(match_type)
+          {
+          case 0:
+	    res = US"was no match"; break;
+          case MT_NOT:
+	    res = US"was an exclude match"; break;
+          case MT_ALL:
+	    res = US"was an IP address that did not match"; break;
+          case MT_NOT|MT_ALL:
+	    res = US"were no IP addresses that did not match"; break;
+          }
+        debug_printf("=> but we are not accepting this block class because\n");
+        debug_printf("=> there %s for %s%c%s\n",
+          res,
+          ((match_type & MT_ALL) == 0)? "" : "=",
+          bitmask? '&' : '=', iplist);
+        }
+      return FAIL;
+      }
+    }
+
+  /* Either there was no IP list, or the record matched, implying that the
+  domain is on the list. We now want to find a corresponding TXT record. If an
+  alternate domain is specified for the TXT record, call this function
+  recursively to look that up; this has the side effect of re-checking that
+  there is indeed an A record at the alternate domain. */
+
+  if (domain_txt != domain)
+    return one_check_dnsbl(domain_txt, domain_txt, keydomain, prepend, NULL,
+      FALSE, match_type, defer_return);
+
+  /* If there is no alternate domain, look up a TXT record in the main domain
+  if it has not previously been cached. */
+
+  if (!cb->text_set)
+    {
+    cb->text_set = TRUE;
+    if (dns_basic_lookup(&dnsa, query, T_TXT) == DNS_SUCCEED)
+      {
+      dns_record *rr;
+      for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
+           rr;
+           rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
+        if (rr->type == T_TXT) break;
+      if (rr)
+        {
+        int len = (rr->data)[0];
+        if (len > 511) len = 127;
+        store_pool = POOL_PERM;
+        cb->text = string_sprintf("%.*s", len, CUS (rr->data+1));
+        store_pool = old_pool;
+        }
+      }
+    }
+
+  dnslist_value = addlist;
+  dnslist_text = cb->text;
+  return OK;
+  }
+
+/* There was a problem with the DNS lookup */
+
+if (cb->rc != DNS_NOMATCH && cb->rc != DNS_NODATA)
+  {
+  log_write(L_dnslist_defer, LOG_MAIN,
+    "DNS list lookup defer (probably timeout) for %s: %s", query,
+    (defer_return == OK)?   US"assumed in list" :
+    (defer_return == FAIL)? US"assumed not in list" :
+                            US"returned DEFER");
+  return defer_return;
+  }
+
+/* No entry was found in the DNS; continue for next domain */
+
+HDEBUG(D_dnsbl)
+  {
+  debug_printf("DNS lookup for %s failed\n", query);
+  debug_printf("=> that means %s is not listed at %s\n",
+     keydomain, domain);
+  }
+
+return FAIL;
+}
+
+
+
+
+/*************************************************
+*        Check host against DNS black lists      *
+*************************************************/
+
+/* This function runs checks against a list of DNS black lists, until one
+matches. Each item on the list can be of the form
+
+  domain=ip-address/key
+
+The domain is the right-most domain that is used for the query, for example,
+blackholes.mail-abuse.org. If the IP address is present, there is a match only
+if the DNS lookup returns a matching IP address. Several addresses may be
+given, comma-separated, for example: x.y.z=127.0.0.1,127.0.0.2.
+
+If no key is given, what is looked up in the domain is the inverted IP address
+of the current client host. If a key is given, it is used to construct the
+domain for the lookup. For example:
+
+  dsn.rfc-ignorant.org/$sender_address_domain
+
+After finding a match in the DNS, the domain is placed in $dnslist_domain, and
+then we check for a TXT record for an error message, and if found, save its
+value in $dnslist_text. We also cache everything in a tree, to optimize
+multiple lookups.
+
+The TXT record is normally looked up in the same domain as the A record, but
+when many lists are combined in a single DNS domain, this will not be a very
+specific message. It is possible to specify a different domain for looking up
+TXT records; this is given before the main domain, comma-separated. For
+example:
+
+  dnslists = http.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.2 : \
+             socks.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.3
+
+The caching ensures that only one lookup in dnsbl.sorbs.net is done.
+
+Note: an address for testing RBL is 192.203.178.39
+Note: an address for testing DUL is 192.203.178.4
+Note: a domain for testing RFCI is example.tld.dsn.rfc-ignorant.org
+
+Arguments:
+  where        the acl type
+  listptr      the domain/address/data list
+  log_msgptr   log message on error
+
+Returns:    OK      successful lookup (i.e. the address is on the list), or
+                      lookup deferred after +include_unknown
+            FAIL    name not found, or no data found for the given type, or
+                      lookup deferred after +exclude_unknown (default)
+            DEFER   lookup failure, if +defer_unknown was set
+*/
+
+int
+verify_check_dnsbl(int where, const uschar ** listptr, uschar ** log_msgptr)
+{
+int sep = 0;
+int defer_return = FAIL;
+const uschar *list = *listptr;
+uschar *domain;
+uschar *s;
+uschar buffer[1024];
+uschar revadd[128];        /* Long enough for IPv6 address */
+
+/* Indicate that the inverted IP address is not yet set up */
+
+revadd[0] = 0;
+
+/* In case this is the first time the DNS resolver is being used. */
+
+dns_init(FALSE, FALSE, FALSE);	/*XXX dnssec? */
+
+/* Loop through all the domains supplied, until something matches */
+
+while ((domain = string_nextinlist(&list, &sep, buffer, sizeof(buffer))) != NULL)
+  {
+  int rc;
+  BOOL bitmask = FALSE;
+  int match_type = 0;
+  uschar *domain_txt;
+  uschar *comma;
+  uschar *iplist;
+  uschar *key;
+
+  HDEBUG(D_dnsbl) debug_printf("DNS list check: %s\n", domain);
+
+  /* Deal with special values that change the behaviour on defer */
+
+  if (domain[0] == '+')
+    {
+    if      (strcmpic(domain, US"+include_unknown") == 0) defer_return = OK;
+    else if (strcmpic(domain, US"+exclude_unknown") == 0) defer_return = FAIL;
+    else if (strcmpic(domain, US"+defer_unknown") == 0)   defer_return = DEFER;
+    else
+      log_write(0, LOG_MAIN|LOG_PANIC, "unknown item in dnslist (ignored): %s",
+        domain);
+    continue;
+    }
+
+  /* See if there's explicit data to be looked up */
+
+  if ((key = Ustrchr(domain, '/'))) *key++ = 0;
+
+  /* See if there's a list of addresses supplied after the domain name. This is
+  introduced by an = or a & character; if preceded by = we require all matches
+  and if preceded by ! we invert the result. */
+
+  if (!(iplist = Ustrchr(domain, '=')))
+    {
+    bitmask = TRUE;
+    iplist = Ustrchr(domain, '&');
+    }
+
+  if (iplist)				       /* Found either = or & */
+    {
+    if (iplist > domain && iplist[-1] == '!')  /* Handle preceding ! */
+      {
+      match_type |= MT_NOT;
+      iplist[-1] = 0;
+      }
+
+    *iplist++ = 0;                             /* Terminate domain, move on */
+
+    /* If we found = (bitmask == FALSE), check for == or =& */
+
+    if (!bitmask && (*iplist == '=' || *iplist == '&'))
+      {
+      bitmask = *iplist++ == '&';
+      match_type |= MT_ALL;
+      }
+    }
+
+
+  /* If there is a comma in the domain, it indicates that a second domain for
+  looking up TXT records is provided, before the main domain. Otherwise we must
+  set domain_txt == domain. */
+
+  domain_txt = domain;
+  comma = Ustrchr(domain, ',');
+  if (comma != NULL)
+    {
+    *comma++ = 0;
+    domain = comma;
+    }
+
+  /* Check that what we have left is a sensible domain name. There is no reason
+  why these domains should in fact use the same syntax as hosts and email
+  domains, but in practice they seem to. However, there is little point in
+  actually causing an error here, because that would no doubt hold up incoming
+  mail. Instead, I'll just log it. */
+
+  for (s = domain; *s != 0; s++)
+    {
+    if (!isalnum(*s) && *s != '-' && *s != '.' && *s != '_')
+      {
+      log_write(0, LOG_MAIN, "dnslists domain \"%s\" contains "
+        "strange characters - is this right?", domain);
+      break;
+      }
+    }
+
+  /* Check the alternate domain if present */
+
+  if (domain_txt != domain) for (s = domain_txt; *s != 0; s++)
+    {
+    if (!isalnum(*s) && *s != '-' && *s != '.' && *s != '_')
+      {
+      log_write(0, LOG_MAIN, "dnslists domain \"%s\" contains "
+        "strange characters - is this right?", domain_txt);
+      break;
+      }
+    }
+
+  /* If there is no key string, construct the query by adding the domain name
+  onto the inverted host address, and perform a single DNS lookup. */
+
+  if (key == NULL)
+    {
+    if (where == ACL_WHERE_NOTSMTP_START || where == ACL_WHERE_NOTSMTP)
+      {
+      *log_msgptr = string_sprintf
+	("cannot test auto-keyed dnslists condition in %s ACL",
+	  acl_wherenames[where]);
+      return ERROR;
+      }
+    if (sender_host_address == NULL) return FAIL;    /* can never match */
+    if (revadd[0] == 0) invert_address(revadd, sender_host_address);
+    rc = one_check_dnsbl(domain, domain_txt, sender_host_address, revadd,
+      iplist, bitmask, match_type, defer_return);
+    if (rc == OK)
+      {
+      dnslist_domain = string_copy(domain_txt);
+      dnslist_matched = string_copy(sender_host_address);
+      HDEBUG(D_dnsbl) debug_printf("=> that means %s is listed at %s\n",
+        sender_host_address, dnslist_domain);
+      }
+    if (rc != FAIL) return rc;     /* OK or DEFER */
+    }
+
+  /* If there is a key string, it can be a list of domains or IP addresses to
+  be concatenated with the main domain. */
+
+  else
+    {
+    int keysep = 0;
+    BOOL defer = FALSE;
+    uschar *keydomain;
+    uschar keybuffer[256];
+    uschar keyrevadd[128];
+
+    while ((keydomain = string_nextinlist(CUSS &key, &keysep, keybuffer,
+            sizeof(keybuffer))) != NULL)
+      {
+      uschar *prepend = keydomain;
+
+      if (string_is_ip_address(keydomain, NULL) != 0)
+        {
+        invert_address(keyrevadd, keydomain);
+        prepend = keyrevadd;
+        }
+
+      rc = one_check_dnsbl(domain, domain_txt, keydomain, prepend, iplist,
+        bitmask, match_type, defer_return);
+
+      if (rc == OK)
+        {
+        dnslist_domain = string_copy(domain_txt);
+        dnslist_matched = string_copy(keydomain);
+        HDEBUG(D_dnsbl) debug_printf("=> that means %s is listed at %s\n",
+          keydomain, dnslist_domain);
+        return OK;
+        }
+
+      /* If the lookup deferred, remember this fact. We keep trying the rest
+      of the list to see if we get a useful result, and if we don't, we return
+      DEFER at the end. */
+
+      if (rc == DEFER) defer = TRUE;
+      }    /* continue with next keystring domain/address */
+
+    if (defer) return DEFER;
+    }
+  }        /* continue with next dnsdb outer domain */
+
+return FAIL;
+}
+
+/* vi: aw ai sw=2
+*/
+/* End of verify.c */