Adding upstream version 3.8.5.upstream/3.8.5

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

1 files changed, 864 insertions, 0 deletions

diff --git a/src/smtp/smtp_addr.c b/src/smtp/smtp_addr.c
new file mode 100644
index 0000000..5e23388
--- /dev/null
+++ b/src/smtp/smtp_addr.c
@@ -0,0 +1,864 @@
+/*++
+/* NAME
+/*	smtp_addr 3
+/* SUMMARY
+/*	SMTP server address lookup
+/* SYNOPSIS
+/*	#include "smtp_addr.h"
+/*
+/*	DNS_RR *smtp_domain_addr(name, mxrr, misc_flags, why, found_myself)
+/*	char	*name;
+/*	DNS_RR  **mxrr;
+/*	int	misc_flags;
+/*	DSN_BUF	*why;
+/*	int	*found_myself;
+/*
+/*	DNS_RR *smtp_host_addr(name, misc_flags, why)
+/*	char	*name;
+/*	int	misc_flags;
+/*	DSN_BUF	*why;
+/*
+/*	DNS_RR	*smtp_service_addr(name, service, mxrr, misc_flags, why,
+/*					found_myself)
+/*	const char *name;
+/*	const char *service;
+/*	DNS_RR  **mxrr;
+/*	int	misc_flags;
+/*	DSN_BUF	*why;
+/*	int	*found_myself;
+/* DESCRIPTION
+/*	This module implements Internet address lookups. By default,
+/*	lookups are done via the Internet domain name service (DNS).
+/*	A reasonable number of CNAME indirections is permitted. When
+/*	DNS lookups are disabled, host address lookup is done with
+/*	getnameinfo() or gethostbyname().
+/*
+/*	smtp_domain_addr() looks up the network addresses for mail
+/*	exchanger hosts listed for the named domain. Addresses are
+/*	returned in most-preferred first order. The result is truncated
+/*	so that it contains only hosts that are more preferred than the
+/*	local mail server itself. The found_myself result parameter
+/*	is updated when the local MTA is MX host for the specified
+/*	destination.  If MX records were found, the rname, qname,
+/*	and dnssec validation status of the MX RRset are returned
+/*	via mxrr, which the caller must free with dns_rr_free().
+/*	Fallback from MX to address lookups is governed by RFC 2821,
+/*	and by local policy (var_ign_mx_lookup_err).
+/*
+/*	When no mail exchanger is listed in the DNS for \fIname\fR, the
+/*	request is passed to smtp_host_addr().
+/*
+/*	It is an error to call smtp_domain_addr() when DNS lookups are
+/*	disabled.
+/*
+/*	smtp_host_addr() looks up all addresses listed for the named
+/*	host.  The host can be specified as a numerical Internet network
+/*	address, or as a symbolic host name.
+/*
+/*	smtp_service_addr() looks up addresses for hosts specified
+/*	in SRV records for the specified domain and service. This
+/*	supports the features of smtp_domain_addr() except that
+/*	the order of SRV records is determined by RFC 2782, and
+/*	that address records are not sorted by IP address family
+/*	preference.  Fallback from SRV to MX or address lookups is
+/*	governed by local policy (var_ign_mx_lookup_err and
+/*	var_allow_srv_fallback).
+/*
+/*	Results from smtp_domain_addr(), smtp_host_addr(), and
+/*	smtp_service_addr() are destroyed by dns_rr_free(), including
+/*	null lists.
+/* DIAGNOSTICS
+/*	Panics: interface violations. For example, calling smtp_domain_addr()
+/*	when DNS lookups are explicitly disabled.
+/*
+/*	All routines either return a DNS_RR pointer, or return a null
+/*	pointer and update the \fIwhy\fR argument accordingly.
+/* LICENSE
+/* .ad
+/* .fi
+/*	The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/*	Wietse Venema
+/*	IBM T.J. Watson Research
+/*	P.O. Box 704
+/*	Yorktown Heights, NY 10598, USA
+/*
+/*	Wietse Venema
+/*	Google, Inc.
+/*	111 8th Avenue
+/*	New York, NY 10011, USA
+/*
+/*	SRV Support by
+/*	Tomas Korbar
+/*	Red Hat, Inc.
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <stdlib.h>
+#include <netdb.h>
+#include <ctype.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+
+/* Utility library. */
+
+#include <msg.h>
+#include <vstring.h>
+#include <mymalloc.h>
+#include <inet_addr_list.h>
+#include <stringops.h>
+#include <myaddrinfo.h>
+#include <inet_proto.h>
+#include <midna_domain.h>
+
+/* Global library. */
+
+#include <mail_params.h>
+#include <own_inet_addr.h>
+#include <dsn_buf.h>
+
+/* DNS library. */
+
+#include <dns.h>
+
+/* Application-specific. */
+
+#include "smtp.h"
+#include "smtp_addr.h"
+
+/* smtp_print_addr - print address list */
+
+static void smtp_print_addr(const char *what, DNS_RR *addr_list)
+{
+    DNS_RR *addr;
+    MAI_HOSTADDR_STR hostaddr;
+
+    msg_info("begin %s address list", what);
+    for (addr = addr_list; addr; addr = addr->next) {
+	if (dns_rr_to_pa(addr, &hostaddr) == 0) {
+	    msg_warn("skipping record type %s: %m", dns_strtype(addr->type));
+	} else {
+	    msg_info("pref %4d host %s/%s",
+		     addr->pref, SMTP_HNAME(addr),
+		     hostaddr.buf);
+	}
+    }
+    msg_info("end %s address list", what);
+}
+
+/* smtp_addr_one - address lookup for one host name */
+
+static DNS_RR *smtp_addr_one(DNS_RR *addr_list, const char *host, int res_opt,
+			             unsigned pref, unsigned port,
+			             DSN_BUF *why)
+{
+    const char *myname = "smtp_addr_one";
+    DNS_RR *addr = 0;
+    DNS_RR *rr;
+    int     aierr;
+    struct addrinfo *res0;
+    struct addrinfo *res;
+    const INET_PROTO_INFO *proto_info = inet_proto_info();
+    unsigned char *proto_family_list = proto_info->sa_family_list;
+    int     found;
+
+    if (msg_verbose)
+	msg_info("%s: host %s", myname, host);
+
+    /*
+     * Interpret a numerical name as an address.
+     */
+    if (hostaddr_to_sockaddr(host, (char *) 0, 0, &res0) == 0) {
+	if (strchr((char *) proto_family_list, res0->ai_family) != 0) {
+	    if ((addr = dns_sa_to_rr(host, pref, res0->ai_addr)) == 0)
+		msg_fatal("host %s: conversion error for address family "
+			  "%d: %m", host, res0->ai_addr->sa_family);
+	    addr_list = dns_rr_append(addr_list, addr);
+	    addr->pref = pref;
+	    addr->port = port;
+	    if (msg_verbose)
+		msg_info("%s: using numerical host %s", myname, host);
+	    freeaddrinfo(res0);
+	    return (addr_list);
+	}
+	freeaddrinfo(res0);
+    }
+
+    /*
+     * Use DNS lookup, but keep the option open to use native name service.
+     * 
+     * XXX A soft error dominates past and future hard errors. Therefore we
+     * should not clobber a soft error text and status code.
+     */
+    if (smtp_host_lookup_mask & SMTP_HOST_FLAG_DNS) {
+	res_opt |= smtp_dns_res_opt;
+	switch (dns_lookup_v(host, res_opt, &addr, (VSTRING *) 0,
+			     why->reason, DNS_REQ_FLAG_NONE,
+			     proto_info->dns_atype_list)) {
+	case DNS_OK:
+	    for (rr = addr; rr; rr = rr->next) {
+		rr->pref = pref;
+		rr->port = port;
+	    }
+	    addr_list = dns_rr_append(addr_list, addr);
+	    return (addr_list);
+	default:
+	    dsb_status(why, "4.4.3");
+	    return (addr_list);
+	case DNS_FAIL:
+	    dsb_status(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.3" : "5.4.3");
+	    return (addr_list);
+	case DNS_INVAL:
+	    dsb_status(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.4" : "5.4.4");
+	    return (addr_list);
+	case DNS_POLICY:
+	    dsb_status(why, "4.7.0");
+	    return (addr_list);
+	case DNS_NOTFOUND:
+	    dsb_status(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.4" : "5.4.4");
+	    /* maybe native naming service will succeed */
+	    break;
+	}
+    }
+
+    /*
+     * Use the native name service which also looks in /etc/hosts.
+     * 
+     * XXX A soft error dominates past and future hard errors. Therefore we
+     * should not clobber a soft error text and status code.
+     */
+#define RETRY_AI_ERROR(e) \
+        ((e) == EAI_AGAIN || (e) == EAI_MEMORY || (e) == EAI_SYSTEM)
+#ifdef EAI_NODATA
+#define DSN_NOHOST(e) \
+	((e) == EAI_AGAIN || (e) == EAI_NODATA || (e) == EAI_NONAME)
+#else
+#define DSN_NOHOST(e) \
+	((e) == EAI_AGAIN || (e) == EAI_NONAME)
+#endif
+
+    if (smtp_host_lookup_mask & SMTP_HOST_FLAG_NATIVE) {
+	if ((aierr = hostname_to_sockaddr(host, (char *) 0, 0, &res0)) != 0) {
+	    dsb_simple(why, (SMTP_HAS_SOFT_DSN(why) || RETRY_AI_ERROR(aierr)) ?
+		       (DSN_NOHOST(aierr) ? "4.4.4" : "4.3.0") :
+		       (DSN_NOHOST(aierr) ? "5.4.4" : "5.3.0"),
+		       "unable to look up host %s: %s",
+		       host, MAI_STRERROR(aierr));
+	} else {
+	    for (found = 0, res = res0; res != 0; res = res->ai_next) {
+		if (strchr((char *) proto_family_list, res->ai_family) == 0) {
+		    msg_info("skipping address family %d for host %s",
+			     res->ai_family, host);
+		    continue;
+		}
+		found++;
+		if ((addr = dns_sa_to_rr(host, pref, res->ai_addr)) == 0)
+		    msg_fatal("host %s: conversion error for address family "
+			      "%d: %m", host, res0->ai_addr->sa_family);
+		addr_list = dns_rr_append(addr_list, addr);
+		if (msg_verbose) {
+		    MAI_HOSTADDR_STR hostaddr_str;
+
+		    SOCKADDR_TO_HOSTADDR(res->ai_addr, res->ai_addrlen,
+				  &hostaddr_str, (MAI_SERVPORT_STR *) 0, 0);
+		    msg_info("%s: native lookup result: %s",
+			     myname, hostaddr_str.buf);
+		}
+	    }
+	    freeaddrinfo(res0);
+	    if (found == 0) {
+		dsb_simple(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.4" : "5.4.4",
+			   "%s: host not found", host);
+	    }
+	    return (addr_list);
+	}
+    }
+
+    /*
+     * No further alternatives for host lookup.
+     */
+    return (addr_list);
+}
+
+/* smtp_addr_list - address lookup for a list of mail exchangers */
+
+static DNS_RR *smtp_addr_list(DNS_RR *mx_names, DSN_BUF *why)
+{
+    DNS_RR *addr_list = 0;
+    DNS_RR *rr;
+    int     res_opt = 0;
+
+    if (mx_names->dnssec_valid)
+	res_opt = RES_USE_DNSSEC;
+#ifdef USE_TLS
+    else if (smtp_tls_insecure_mx_policy > TLS_LEV_MAY)
+	res_opt = RES_USE_DNSSEC;
+#endif
+
+    /*
+     * As long as we are able to look up any host address, we ignore problems
+     * with DNS lookups (except if we're backup MX, and all the better MX
+     * hosts can't be found).
+     * 
+     * XXX 2821: update the error status (0->FAIL upon unrecoverable lookup
+     * error, any->RETRY upon temporary lookup error) so that we can
+     * correctly handle the case of no resolvable MX host. Currently this is
+     * always treated as a soft error. RFC 2821 wants a more precise
+     * response.
+     * 
+     * XXX dns_lookup() enables RES_DEFNAMES. This is wrong for names found in
+     * MX records - we should not append the local domain to dot-less names.
+     * 
+     * XXX However, this is not the only problem. If we use the native name
+     * service for host lookup, then it will usually enable RES_DNSRCH which
+     * appends local domain information to all lookups. In particular,
+     * getaddrinfo() may invoke a resolver that runs in a different process
+     * (NIS server, nscd), so we can't even reliably turn this off by
+     * tweaking the in-process resolver flags.
+     */
+    for (rr = mx_names; rr; rr = rr->next) {
+	if (rr->type != T_MX && rr->type != T_SRV)
+	    msg_panic("smtp_addr_list: bad resource type: %d", rr->type);
+	addr_list = smtp_addr_one(addr_list, (char *) rr->data, res_opt,
+				  rr->pref, rr->port, why);
+    }
+    return (addr_list);
+}
+
+/* smtp_find_self - spot myself in a crowd of mail exchangers */
+
+static DNS_RR *smtp_find_self(DNS_RR *addr_list)
+{
+    const char *myname = "smtp_find_self";
+    INET_ADDR_LIST *self;
+    INET_ADDR_LIST *proxy;
+    DNS_RR *addr;
+    int     i;
+
+    self = own_inet_addr_list();
+    proxy = proxy_inet_addr_list();
+
+    for (addr = addr_list; addr; addr = addr->next) {
+
+	/*
+	 * Find out if this mail system is listening on this address.
+	 */
+	for (i = 0; i < self->used; i++)
+	    if (DNS_RR_EQ_SA(addr, (struct sockaddr *) (self->addrs + i))) {
+		if (msg_verbose)
+		    msg_info("%s: found self at pref %d", myname, addr->pref);
+		return (addr);
+	    }
+
+	/*
+	 * Find out if this mail system has a proxy listening on this
+	 * address.
+	 */
+	for (i = 0; i < proxy->used; i++)
+	    if (DNS_RR_EQ_SA(addr, (struct sockaddr *) (proxy->addrs + i))) {
+		if (msg_verbose)
+		    msg_info("%s: found proxy at pref %d", myname, addr->pref);
+		return (addr);
+	    }
+    }
+
+    /*
+     * Didn't find myself, or my proxy.
+     */
+    if (msg_verbose)
+	msg_info("%s: not found", myname);
+    return (0);
+}
+
+/* smtp_truncate_self - truncate address list at self and equivalents */
+
+static DNS_RR *smtp_truncate_self(DNS_RR *addr_list, unsigned pref)
+{
+    DNS_RR *addr;
+    DNS_RR *last;
+
+    for (last = 0, addr = addr_list; addr; last = addr, addr = addr->next) {
+	if (pref == addr->pref) {
+	    if (msg_verbose)
+		smtp_print_addr("truncated", addr);
+	    dns_rr_free(addr);
+	    if (last == 0) {
+		addr_list = 0;
+	    } else {
+		last->next = 0;
+	    }
+	    break;
+	}
+    }
+    return (addr_list);
+}
+
+/* smtp_balance_inet_proto - balance IPv4/6 protocols within address limit */
+
+static DNS_RR *smtp_balance_inet_proto(DNS_RR *addr_list, int misc_flags,
+				               int addr_limit)
+{
+    const char myname[] = "smtp_balance_inet_proto";
+    DNS_RR *rr;
+    DNS_RR *stripped_list;
+    DNS_RR *next;
+    int     v6_count;
+    int     v4_count;
+    int     v6_target, v4_target;
+    int    *p;
+
+    /*
+     * Precondition: the input is sorted by MX preference (not necessarily IP
+     * address family preference), and addresses with the same or worse
+     * preference than 'myself' have been eliminated. Postcondition: the
+     * relative list order is unchanged, but some elements are removed.
+     */
+
+    /*
+     * Count the number of IPv6 and IPv4 addresses.
+     */
+    for (v4_count = v6_count = 0, rr = addr_list; rr != 0; rr = rr->next) {
+	if (rr->type == T_A) {
+	    v4_count++;
+	} else if (rr->type == T_AAAA) {
+	    v6_count++;
+	} else {
+	    msg_panic("%s: unexpected record type: %s",
+		      myname, dns_strtype(rr->type));
+	}
+    }
+
+    /*
+     * Ensure that one address type will not out-crowd the other, while
+     * enforcing the address count limit. This works around a current problem
+     * where some destination announces primarily IPv6 MX addresses, the
+     * smtp_address_limit eliminates most or all IPv4 addresses, and the
+     * destination is not reachable over IPv6.
+     * 
+     * Maybe: do all smtp_mx_address_limit enforcement here, and remove
+     * pre-existing enforcement elsewhere. That would obsolete the
+     * smtp_balance_inet_protocols configuration parameter.
+     */
+    if (v4_count > 0 && v6_count > 0 && v4_count + v6_count > addr_limit) {
+
+	/*-
+         * Decide how many IPv6 and IPv4 addresses to keep. The code below
+         * has three branches, corresponding to the regions R1, R2 and R3
+         * in the figure.
+         *
+         *  L = addr_limit
+         *  X = excluded by condition (v4_count + v6_count > addr_limit)
+         *
+         * v4_count
+         *     ^
+         *     |
+         *  L  \  R1
+         *     |X\     |
+         *     |XXX\   |
+         *     |XXXXX\ | R2
+         * L/2 +-------\-------
+         *     |XXXXXXX|X\
+         *     |XXXXXXX|XXX\  R3
+         *     |XXXXXXX|XXXXX\
+         *   0 +-------+-------\--> v6_count
+         *     0      L/2      L
+         */
+	if (v6_count <= addr_limit / 2) {	/* Region R1 */
+	    v6_target = v6_count;
+	    v4_target = addr_limit - v6_target;
+	} else if (v4_count <= addr_limit / 2) {/* Region R3 */
+	    v4_target = v4_count;
+	    v6_target = addr_limit - v4_target;
+	} else {				/* Region R2 */
+	    /* v4_count > addr_limit / 2 && v6_count > addr_limit / 2 */
+	    v4_target = (addr_limit + (addr_list->type == T_A)) / 2;
+	    v6_target = addr_limit - v4_target;
+	}
+	if (msg_verbose)
+	    msg_info("v6_target=%d, v4_target=%d", v6_target, v4_target);
+
+	/* Enforce the address count targets. */
+	stripped_list = 0;
+	for (rr = addr_list; rr != 0; rr = next) {
+	    next = rr->next;
+	    rr->next = 0;
+	    if (rr->type == T_A) {
+		p = &v4_target;
+	    } else if (rr->type == T_AAAA) {
+		p = &v6_target;
+	    } else {
+		msg_panic("%s: unexpected record type: %s",
+			  myname, dns_strtype(rr->type));
+	    }
+	    if (*p > 0) {
+		stripped_list = dns_rr_append(stripped_list, rr);
+		*p -= 1;
+	    } else {
+		dns_rr_free(rr);
+	    }
+	}
+	if (v4_target > 0 || v6_target > 0)
+	    msg_panic("%s: bad target count: v4_target=%d, v6_target=%d",
+		      myname, v4_target, v6_target);
+	if (msg_verbose)
+	    smtp_print_addr("smtp_balance_inet_proto result", stripped_list);
+	return (stripped_list);
+    } else {
+	return (addr_list);
+    }
+}
+
+/* smtp_domain_addr - mail exchanger address lookup */
+
+DNS_RR *smtp_domain_addr(const char *name, DNS_RR **mxrr, int misc_flags,
+			         DSN_BUF *why, int *found_myself)
+{
+    DNS_RR *mx_names;
+    DNS_RR *addr_list = 0;
+    DNS_RR *self = 0;
+    unsigned best_pref;
+    unsigned best_found;
+    int     r = 0;			/* Resolver flags */
+    const char *aname;
+
+    dsb_reset(why);				/* Paranoia */
+
+    /*
+     * Preferences from DNS use 0..32767, fall-backs use 32768+.
+     */
+#define IMPOSSIBLE_PREFERENCE	(~0)
+
+    /*
+     * Sanity check.
+     */
+    if (smtp_dns_support == SMTP_DNS_DISABLED)
+	msg_panic("smtp_domain_addr: DNS lookup is disabled");
+    if (smtp_dns_support == SMTP_DNS_DNSSEC)
+	r |= RES_USE_DNSSEC;
+
+    /*
+     * IDNA support.
+     */
+#ifndef NO_EAI
+    if (!allascii(name) && (aname = midna_domain_to_ascii(name)) != 0) {
+	if (msg_verbose)
+	    msg_info("%s asciified to %s", name, aname);
+    } else
+#endif
+	aname = name;
+
+    /*
+     * Look up the mail exchanger hosts listed for this name. Sort the
+     * results by preference. Look up the corresponding host addresses, and
+     * truncate the list so that it contains only hosts that are more
+     * preferred than myself. When no MX resource records exist, look up the
+     * addresses listed for this name.
+     * 
+     * According to RFC 974: "It is possible that the list of MXs in the
+     * response to the query will be empty.  This is a special case.  If the
+     * list is empty, mailers should treat it as if it contained one RR, an
+     * MX RR with a preference value of 0, and a host name of REMOTE.  (I.e.,
+     * REMOTE is its only MX).  In addition, the mailer should do no further
+     * processing on the list, but should attempt to deliver the message to
+     * REMOTE."
+     * 
+     * Normally it is OK if an MX host cannot be found in the DNS; we'll just
+     * use a backup one, and silently ignore the better MX host. However, if
+     * the best backup that we can find in the DNS is the local machine, then
+     * we must remember that the local machine is not the primary MX host, or
+     * else we will claim that mail loops back.
+     * 
+     * XXX Optionally do A lookups even when the MX lookup didn't complete.
+     * Unfortunately with some DNS servers this is not a transient problem.
+     * 
+     * XXX Ideally we would perform A lookups only as far as needed. But as long
+     * as we're looking up all the hosts, it would be better to look up the
+     * least preferred host first, so that DNS lookup error messages make
+     * more sense.
+     * 
+     * XXX 2821: RFC 2821 says that the sender must shuffle equal-preference MX
+     * hosts, whereas multiple A records per hostname must be used in the
+     * order as received. They make the bogus assumption that a hostname with
+     * multiple A records corresponds to one machine with multiple network
+     * interfaces.
+     * 
+     * XXX 2821: Postfix recognizes the local machine by looking for its own IP
+     * address in the list of mail exchangers. RFC 2821 says one has to look
+     * at the mail exchanger hostname as well, making the bogus assumption
+     * that an IP address is listed only under one hostname. However, looking
+     * at hostnames provides a partial solution for MX hosts behind a NAT
+     * gateway.
+     */
+    switch (dns_lookup(aname, T_MX, r, &mx_names, (VSTRING *) 0, why->reason)) {
+    default:
+	dsb_status(why, "4.4.3");
+	if (var_ign_mx_lookup_err)
+	    addr_list = smtp_host_addr(aname, misc_flags, why);
+	break;
+    case DNS_INVAL:
+	dsb_status(why, "5.4.4");
+	if (var_ign_mx_lookup_err)
+	    addr_list = smtp_host_addr(aname, misc_flags, why);
+	break;
+    case DNS_NULLMX:
+	dsb_status(why, "5.1.0");
+	break;
+    case DNS_POLICY:
+	dsb_status(why, "4.7.0");
+	break;
+    case DNS_FAIL:
+	dsb_status(why, "5.4.3");
+	if (var_ign_mx_lookup_err)
+	    addr_list = smtp_host_addr(aname, misc_flags, why);
+	break;
+    case DNS_OK:
+	mx_names = dns_rr_sort(mx_names, dns_rr_compare_pref_any);
+	best_pref = (mx_names ? mx_names->pref : IMPOSSIBLE_PREFERENCE);
+	addr_list = smtp_addr_list(mx_names, why);
+	if (mxrr)
+	    *mxrr = dns_rr_copy(mx_names);	/* copies one record! */
+	dns_rr_free(mx_names);
+	if (addr_list == 0) {
+	    /* Text does not change. */
+	    if (var_smtp_defer_mxaddr) {
+		/* Don't clobber the null terminator. */
+		if (SMTP_HAS_HARD_DSN(why))
+		    SMTP_SET_SOFT_DSN(why);	/* XXX */
+		/* Require some error status. */
+		else if (!SMTP_HAS_SOFT_DSN(why))
+		    msg_panic("smtp_domain_addr: bad status");
+	    }
+	    msg_warn("no MX host for %s has a valid address record", name);
+	    break;
+	}
+	best_found = (addr_list ? addr_list->pref : IMPOSSIBLE_PREFERENCE);
+	if (msg_verbose)
+	    smtp_print_addr(name, addr_list);
+	if ((misc_flags & SMTP_MISC_FLAG_LOOP_DETECT)
+	    && (self = smtp_find_self(addr_list)) != 0) {
+	    addr_list = smtp_truncate_self(addr_list, self->pref);
+	    if (addr_list == 0) {
+		if (best_pref != best_found) {
+		    dsb_simple(why, "4.4.4",
+			       "unable to find primary relay for %s", name);
+		} else {
+		    dsb_simple(why, "5.4.6", "mail for %s loops back to myself",
+			       name);
+		}
+	    }
+	}
+#define SMTP_COMPARE_ADDR(flags) \
+	(((flags) & SMTP_MISC_FLAG_PREF_IPV6) ? dns_rr_compare_pref_ipv6 : \
+	 ((flags) & SMTP_MISC_FLAG_PREF_IPV4) ? dns_rr_compare_pref_ipv4 : \
+	 dns_rr_compare_pref_any)
+
+	if (addr_list && addr_list->next) {
+	    if (var_smtp_rand_addr)
+		addr_list = dns_rr_shuffle(addr_list);
+	    addr_list = dns_rr_sort(addr_list, SMTP_COMPARE_ADDR(misc_flags));
+	    if (var_smtp_mxaddr_limit > 0 && var_smtp_balance_inet_proto)
+		addr_list = smtp_balance_inet_proto(addr_list, misc_flags,
+						    var_smtp_mxaddr_limit);
+	}
+	break;
+    case DNS_NOTFOUND:
+	addr_list = smtp_host_addr(aname, misc_flags, why);
+	break;
+    }
+
+    /*
+     * Clean up.
+     */
+    *found_myself |= (self != 0);
+    return (addr_list);
+}
+
+/* smtp_host_addr - direct host lookup */
+
+DNS_RR *smtp_host_addr(const char *host, int misc_flags, DSN_BUF *why)
+{
+    DNS_RR *addr_list;
+    int     res_opt = 0;
+    const char *ahost;
+
+    dsb_reset(why);				/* Paranoia */
+
+    if (smtp_dns_support == SMTP_DNS_DNSSEC)
+	res_opt |= RES_USE_DNSSEC;
+
+    /*
+     * IDNA support.
+     */
+#ifndef NO_EAI
+    if (!allascii(host) && (ahost = midna_domain_to_ascii(host)) != 0) {
+	if (msg_verbose)
+	    msg_info("%s asciified to %s", host, ahost);
+    } else
+#endif
+	ahost = host;
+
+    /*
+     * If the host is specified by numerical address, just convert the
+     * address to internal form. Otherwise, the host is specified by name.
+     */
+#define PREF0	0
+    addr_list = smtp_addr_one((DNS_RR *) 0, ahost, res_opt, PREF0, 0, why);
+    if (addr_list
+	&& (misc_flags & SMTP_MISC_FLAG_LOOP_DETECT)
+	&& smtp_find_self(addr_list) != 0) {
+	dns_rr_free(addr_list);
+	dsb_simple(why, "5.4.6", "mail for %s loops back to myself", host);
+	return (0);
+    }
+    if (addr_list && addr_list->next) {
+	if (var_smtp_rand_addr)
+	    addr_list = dns_rr_shuffle(addr_list);
+	/* The following changes the order of equal-preference hosts. */
+	if (inet_proto_info()->ai_family_list[1] != 0)
+	    addr_list = dns_rr_sort(addr_list, SMTP_COMPARE_ADDR(misc_flags));
+	if (var_smtp_mxaddr_limit > 0 && var_smtp_balance_inet_proto)
+	    addr_list = smtp_balance_inet_proto(addr_list, misc_flags,
+						var_smtp_mxaddr_limit);
+    }
+    if (msg_verbose)
+	smtp_print_addr(host, addr_list);
+    return (addr_list);
+}
+
+/* smtp_service_addr - service address lookup */
+
+DNS_RR *smtp_service_addr(const char *name, const char *service, DNS_RR **mxrr,
+			          int misc_flags, DSN_BUF *why,
+			          int *found_myself)
+{
+    static VSTRING *srv_qname = 0;
+    const char *str_srv_qname;
+    DNS_RR *srv_names = 0;
+    DNS_RR *addr_list = 0;
+    DNS_RR *self = 0;
+    unsigned best_pref;
+    unsigned best_found;
+    int     r = 0;
+    const char *aname;
+    int     allow_non_srv_fallback = var_allow_srv_fallback;
+
+    dsb_reset(why);
+
+    /*
+     * Sanity check.
+     */
+    if (smtp_dns_support == SMTP_DNS_DISABLED)
+	msg_panic("smtp_service_addr: DNS lookup is disabled");
+
+    if (smtp_dns_support == SMTP_DNS_DNSSEC) {
+	r |= RES_USE_DNSSEC;
+    }
+    if (srv_qname == 0)
+	srv_qname = vstring_alloc(100);
+    vstring_sprintf(srv_qname, "_%s._tcp.%s", service, name);
+    str_srv_qname = STR(srv_qname);
+
+    /*
+     * IDNA support.
+     */
+#ifndef NO_EAI
+    if (!allascii(str_srv_qname)
+	&& (aname = midna_domain_to_ascii(str_srv_qname)) != 0) {
+	if (msg_verbose)
+	    msg_info("%s asciified to %s", str_srv_qname, aname);
+    } else
+#endif
+	aname = str_srv_qname;
+
+    switch (dns_lookup(aname, T_SRV, r, &srv_names, (VSTRING *) 0,
+		       why->reason)) {
+    default:
+	dsb_status(why, "4.4.3");
+	allow_non_srv_fallback |= var_ign_srv_lookup_err;
+	break;
+    case DNS_INVAL:
+	dsb_status(why, "5.4.4");
+	allow_non_srv_fallback |= var_ign_srv_lookup_err;
+	break;
+    case DNS_POLICY:
+	dsb_status(why, "4.7.0");
+	break;
+    case DNS_FAIL:
+	dsb_status(why, "5.4.3");
+	allow_non_srv_fallback |= var_ign_srv_lookup_err;
+	break;
+    case DNS_NULLSRV:
+	dsb_status(why, "5.1.0");
+	break;
+    case DNS_OK:
+	/* Shuffle then sort the SRV rr records by priority and weight. */
+	srv_names = dns_srv_rr_sort(srv_names);
+	best_pref = (srv_names ? srv_names->pref : IMPOSSIBLE_PREFERENCE);
+	addr_list = smtp_addr_list(srv_names, why);
+	if (mxrr)
+	    *mxrr = dns_rr_copy(srv_names);	/* copies one record! */
+	dns_rr_free(srv_names);
+	if (addr_list == 0) {
+	    msg_warn("no SRV host for %s has a valid address record",
+		     str_srv_qname);
+	    break;
+	}
+	/* Optional loop prevention, similar to smtp_domain_addr(). */
+	best_found = (addr_list ? addr_list->pref : IMPOSSIBLE_PREFERENCE);
+	if (msg_verbose)
+	    smtp_print_addr(aname, addr_list);
+	if ((misc_flags & SMTP_MISC_FLAG_LOOP_DETECT)
+	    && (self = smtp_find_self(addr_list)) != 0) {
+	    addr_list = smtp_truncate_self(addr_list, self->pref);
+	    if (addr_list == 0) {
+		if (best_pref != best_found) {
+		    dsb_simple(why, "4.4.4",
+			       "unable to find primary relay for %s",
+			       str_srv_qname);
+		} else {
+		    dsb_simple(why, "5.4.6", "mail for %s loops back to myself",
+			       str_srv_qname);
+		}
+	    }
+	}
+	/* TODO: sort by priority, weight, and address family preference. */
+
+	/* Optional address family balancing, as in smtp_domain_addr(). */
+	if (addr_list && addr_list->next) {
+	    if (var_smtp_mxaddr_limit > 0 && var_smtp_balance_inet_proto)
+		addr_list = smtp_balance_inet_proto(addr_list, misc_flags,
+						    var_smtp_mxaddr_limit);
+	}
+	break;
+    case DNS_NOTFOUND:
+	dsb_status(why, "5.4.4");
+	break;
+    }
+
+    /*
+     * If permitted, fall back to non-SRV record lookups.
+     */
+    if (addr_list == 0 && allow_non_srv_fallback) {
+	msg_info("skipping SRV lookup for %s: %s",
+		 str_srv_qname, STR(why->reason));
+	if (misc_flags & SMTP_MISC_FLAG_FALLBACK_SRV_TO_MX)
+	    addr_list = smtp_domain_addr(name, mxrr, misc_flags, why,
+					 found_myself);
+	else
+	    addr_list = smtp_host_addr(name, misc_flags, why);
+    }
+
+    /*
+     * Only if we're not falling back.
+     */ 
+    else {
+	*found_myself |= (self != 0);
+    }
+    return (addr_list);
+}