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-rw-r--r--src/smtp/smtp_addr.c693
1 files changed, 693 insertions, 0 deletions
diff --git a/src/smtp/smtp_addr.c b/src/smtp/smtp_addr.c
new file mode 100644
index 0000000..2210ff7
--- /dev/null
+++ b/src/smtp/smtp_addr.c
@@ -0,0 +1,693 @@
+/*++
+/* 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;
+/* 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().
+/*
+/* 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.
+/*
+/* Results from smtp_domain_addr() or smtp_host_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
+/*--*/
+
+/* 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, DSN_BUF *why)
+{
+ const char *myname = "smtp_addr_one";
+ DNS_RR *addr = 0;
+ DNS_RR *rr;
+ int aierr;
+ struct addrinfo *res0;
+ struct addrinfo *res;
+ 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);
+ 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;
+ 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);
+ }
+ 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)
+ 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, 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, 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);
+}