Exim went into a mad DNS lookup loop when doing a callout where the

[exim.git] / src / src / verify.c

/* $Cambridge: exim/src/src/verify.c,v 1.5 2004/11/12 16:54:55 ph10 Exp $ */

/*************************************************
*     Exim - an Internet mail transport agent    *
*************************************************/

/* Copyright (c) University of Cambridge 1995 - 2004 */
/* 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"


/* Structure for caching DNSBL lookups */

typedef struct dnsbl_cache_block {
  dns_address *rhs;
  uschar *text;
  int rc;
  BOOL text_set;
} dnsbl_cache_block;


/* Anchor for DNSBL cache */

static tree_node *dnsbl_cache = NULL;



/*************************************************
*          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, uschar *key, uschar *type,
  int positive_expire, int negative_expire)
{
BOOL negative;
int length, expire;
time_t now;
dbdata_callout_cache *cache_record;

cache_record = dbfn_read_with_length(dbm_file, key, &length);

if (cache_record == NULL)
  {
  HDEBUG(D_verify) debug_printf("callout cache: no %s record found\n", type);
  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\n", type);
  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\n", type);
return cache_record;
}



/*************************************************
*      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_random => do the "random" thing
                      vopt_callout_recipsender => use real sender for recipient
                      vopt_callout_recippmaster => use postmaster for recipient
  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)
{
BOOL is_recipient = (options & vopt_is_recipient) != 0;
BOOL callout_no_cache = (options & vopt_callout_no_cache) != 0;
BOOL callout_random = (options & vopt_callout_random) != 0;

int yield = OK;
BOOL done = FALSE;
uschar *address_key;
uschar *from_address;
uschar *random_local_part = NULL;
uschar **failure_ptr = is_recipient? 
  &recipient_verify_failure : &sender_verify_failure;
open_db dbblock;
open_db *dbm_file = NULL;
dbdata_callout_cache new_domain_record;
dbdata_callout_cache_address new_address_record;
host_item *host;
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. */

address_key = addr->address;
from_address = US"";

if (is_recipient)
  {
  if ((options & vopt_callout_recipsender) != 0)
    {
    address_key = string_sprintf("%s/<%s>", addr->address, sender_address);
    from_address = sender_address;
    }
  else if ((options & vopt_callout_recippmaster) != 0)
    {
    address_key = string_sprintf("%s/<postmaster@%s>", addr->address,
      qualify_domain_sender);
    from_address = string_sprintf("postmaster@%s", qualify_domain_sender);
    }
  }

/* For a sender callout, we must adjust the key if the mailfrom address is not
empty. */

else
  {
  from_address = (se_mailfrom == NULL)? US"" : se_mailfrom;
  if (from_address[0] != 0)
    address_key = string_sprintf("%s/<%s>", addr->address, from_address);
  }

/* Open the callout cache database, it it exists, for reading only at this
stage, unless caching has been disabled. */

if (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)) == NULL)
  {
  HDEBUG(D_verify) debug_printf("callout cache: not available\n");
  }

/* 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. */

if (dbm_file != NULL)
  {
  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 != NULL)
    {
    /* If an early command (up to and including MAIL FROM:<>) was rejected,
    there is no point carrying on. The callout fails. */

    if (cache_record->result == ccache_reject)
      {
      setflag(addr, af_verify_nsfail);
      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"; 
      goto END_CALLOUT;
      }

    /* 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 (callout_random) switch(cache_record->random_result)
      {
      case ccache_accept:
      HDEBUG(D_verify)
        debug_printf("callout cache: domain accepts random addresses\n");
      goto END_CALLOUT;     /* Default yield is OK */

      case ccache_reject:
      HDEBUG(D_verify)
        debug_printf("callout cache: domain rejects random addresses\n");
      callout_random = FALSE;
      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");
      goto END_CACHE;
      }

    /* 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_mailfrom != NULL)
      {
      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).";
        goto END_CALLOUT;
        }
      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");
        goto END_CACHE;
        }

      /* 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_mailfrom = 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).
  */

  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);

  if (cache_address_record != NULL)
    {
    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;
      }
    goto END_CALLOUT;
    }

  /* Close the cache database while we actually do the callout for real. */

  END_CACHE:
  dbfn_close(dbm_file);
  dbm_file = NULL;
  }

/* 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 randomming. */

if (callout_random && callout_random_local_part != NULL)
  {
  random_local_part = expand_string(callout_random_local_part);
  if (random_local_part == NULL)
    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);

/* Now make connections to the hosts and do real callouts. The list of hosts
is passed in as an argument. */

for (host = host_list; host != NULL && !done; host = host->next)
  {
  smtp_inblock inblock;
  smtp_outblock outblock;
  int host_af;
  int port = 25;
  uschar *helo = US"HELO";
  uschar *interface = NULL;  /* Outgoing interface to use; NULL => any */
  uschar inbuffer[4096];
  uschar outbuffer[1024];
  uschar responsebuffer[4096];

  clearflag(addr, af_verify_pmfail);  /* postmaster callout flag */
  clearflag(addr, af_verify_nsfail);  /* null sender callout flag */

  /* Skip this host if we don't have an IP address for it. */

  if (host->address == NULL)
    {
    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, ':') == NULL)? AF_INET:AF_INET6;

  /* Expand and interpret the interface and port strings. 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;
  if (!smtp_get_interface(tf->interface, host_af, addr, NULL, &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);
  deliver_host = deliver_host_address = NULL;

  /* Set HELO string according to the protocol */

  if (Ustrcmp(tf->protocol, "lmtp") == 0) helo = US"LHLO";

  HDEBUG(D_verify) debug_printf("interface=%s port=%d\n", interface, port);

  /* Set up the buffer for reading SMTP response packets. */

  inblock.buffer = inbuffer;
  inblock.buffersize = sizeof(inbuffer);
  inblock.ptr = inbuffer;
  inblock.ptrend = inbuffer;

  /* Set up the buffer for holding SMTP commands while pipelining */

  outblock.buffer = outbuffer;
  outblock.buffersize = sizeof(outbuffer);
  outblock.ptr = outbuffer;
  outblock.cmd_count = 0;
  outblock.authenticating = FALSE;

  /* Connect to the host; on failure, just loop for the next one, but we
  set the error for the last one. Use the callout_connect timeout. */

  inblock.sock = outblock.sock =
    smtp_connect(host, host_af, port, interface, callout_connect, TRUE);
  if (inblock.sock < 0)
    {
    addr->message = string_sprintf("could not connect to %s [%s]: %s",
        host->name, host->address, strerror(errno));
    continue;
    }

  /* Wait for initial response, and then run the initial SMTP commands. The
  smtp_write_command() function leaves its command in big_buffer. This is
  used in error responses. Initialize it in case the connection is
  rejected. */

  Ustrcpy(big_buffer, "initial connection");

  done =
    smtp_read_response(&inblock, responsebuffer, sizeof(responsebuffer),
      '2', callout) &&

    smtp_write_command(&outblock, FALSE, "%s %s\r\n", helo,
      smtp_active_hostname) >= 0 &&
    smtp_read_response(&inblock, responsebuffer, sizeof(responsebuffer),
      '2', callout) &&

    smtp_write_command(&outblock, FALSE, "MAIL FROM:<%s>\r\n",
      from_address) >= 0 &&
    smtp_read_response(&inblock, responsebuffer, sizeof(responsebuffer),
      '2', callout);

  /* If the host gave an initial error, or does not accept HELO or MAIL
  FROM:<>, arrange to cache this information, but don't record anything for an
  I/O error or a defer. Do not cache rejections when a non-empty sender has
  been used, because that blocks the whole domain for all senders. */

  if (!done)
    {
    *failure_ptr = US"mail"; 
    if (errno == 0 && responsebuffer[0] == '5')
      {
      setflag(addr, af_verify_nsfail);
      if (from_address[0] == 0) new_domain_record.result = ccache_reject;
      }
    }

  /* Otherwise, proceed to check a "random" address (if required), then the
  given address, and the postmaster address (if required). Between each check,
  issue RSET, because some servers accept only one recipient after MAIL
  FROM:<>. */

  else
    {
    new_domain_record.result = ccache_accept;

    /* Do the random local part check first */

    if (random_local_part != NULL)
      {
      uschar randombuffer[1024];
      BOOL random_ok =
        smtp_write_command(&outblock, FALSE,
          "RCPT TO:<%.1000s@%.1000s>\r\n", random_local_part,
          addr->domain) >= 0 &&
        smtp_read_response(&inblock, randombuffer,
          sizeof(randombuffer), '2', callout);

      /* Remember when we last did a random test */

      new_domain_record.random_stamp = time(NULL);

      /* If accepted, we aren't going to do any further tests below. */

      if (random_ok)
        {
        new_domain_record.random_result = ccache_accept;
        }

      /* 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. */

      else if (errno == 0)
        {
        if (randombuffer[0] == '5')
          new_domain_record.random_result = ccache_reject;

        done =
          smtp_write_command(&outblock, FALSE, "RSET\r\n") >= 0 &&
          smtp_read_response(&inblock, responsebuffer, sizeof(responsebuffer),
            '2', callout) &&

          smtp_write_command(&outblock, FALSE, "MAIL FROM:<>\r\n") >= 0 &&
          smtp_read_response(&inblock, responsebuffer, sizeof(responsebuffer),
            '2', callout);
        }
      else done = FALSE;    /* Some timeout/connection problem */
      }                     /* Random check */

    /* If the host is accepting all local parts, as determined by the "random"
    check, we don't need to waste time doing any further checking. */

    if (new_domain_record.random_result != ccache_accept && done)
      {
      done =
        smtp_write_command(&outblock, FALSE, "RCPT TO:<%.1000s>\r\n",
          addr->address) >= 0 &&
        smtp_read_response(&inblock, responsebuffer, sizeof(responsebuffer),
          '2', callout);

      if (done)
        new_address_record.result = ccache_accept;
      else if (errno == 0 && responsebuffer[0] == '5')
        {
        *failure_ptr = US"recipient";  
        new_address_record.result = ccache_reject;
        } 

      /* Do postmaster check if requested */

      if (done && pm_mailfrom != NULL)
        {
        done =
          smtp_write_command(&outblock, FALSE, "RSET\r\n") >= 0 &&
          smtp_read_response(&inblock, responsebuffer,
            sizeof(responsebuffer), '2', callout) &&

          smtp_write_command(&outblock, FALSE,
            "MAIL FROM:<%s>\r\n", pm_mailfrom) >= 0 &&
          smtp_read_response(&inblock, responsebuffer,
            sizeof(responsebuffer), '2', callout) &&

          smtp_write_command(&outblock, FALSE,
            "RCPT TO:<postmaster@%.1000s>\r\n", addr->domain) >= 0 &&
          smtp_read_response(&inblock, responsebuffer,
            sizeof(responsebuffer), '2', callout);

        new_domain_record.postmaster_stamp = time(NULL);

        if (done)
          new_domain_record.postmaster_result = ccache_accept;
        else if (errno == 0 && responsebuffer[0] == '5')
          {
          *failure_ptr = US"postmaster"; 
          setflag(addr, af_verify_pmfail);
          new_domain_record.postmaster_result = ccache_reject;
          }
        }
      }           /* Random not accepted */
    }             /* MAIL FROM:<> accepted */

  /* 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. */

  if (!done)
    {
    if (errno == ETIMEDOUT)
      {
      HDEBUG(D_verify) debug_printf("SMTP timeout\n");
      }
    else if (errno == 0)
      {
      if (*responsebuffer == 0) Ustrcpy(responsebuffer, US"connection dropped");

      addr->message =
        string_sprintf("response to \"%s\" from %s [%s] was: %s",
          big_buffer, host->name, host->address,
          string_printing(responsebuffer));

      addr->user_message = is_recipient?
        string_sprintf("Callout verification failed:\n%s", responsebuffer)
        :
        string_sprintf("Called:   %s\nSent:     %s\nResponse: %s",
          host->address, big_buffer, responsebuffer);

      /* Hard rejection ends the process */

      if (responsebuffer[0] == '5')   /* Address rejected */
        {
        yield = FAIL;
        done = TRUE;
        }
      }
    }

  /* End the SMTP conversation and close the connection. */

  (void)smtp_write_command(&outblock, FALSE, "QUIT\r\n");
  close(inblock.sock);
  }    /* 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.

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 or ccache_reject. */

if (!callout_no_cache && new_domain_record.result != ccache_unknown)
  {
  if ((dbm_file = dbfn_open(US"callout", O_RDWR|O_CREAT, &dbblock, FALSE))
       == NULL)
    {
    HDEBUG(D_verify) debug_printf("callout cache: not available\n");
    }
  else
    {
    (void)dbfn_write(dbm_file, addr->domain, &new_domain_record,
      (int)sizeof(dbdata_callout_cache));
    HDEBUG(D_verify) debug_printf("wrote callout cache domain record:\n"
      "  result=%d postmaster=%d random=%d\n",
      new_domain_record.result,
      new_domain_record.postmaster_result,
      new_domain_record.random_result);
    }
  }

/* If a definite result was obtained for the callout, cache it unless caching
is disabled. */

if (done)
  {
  if (!callout_no_cache && new_address_record.result != ccache_unknown)
    {
    if (dbm_file == NULL)
      dbm_file = dbfn_open(US"callout", O_RDWR|O_CREAT, &dbblock, FALSE);
    if (dbm_file == NULL)
      {
      HDEBUG(D_verify) debug_printf("no callout cache available\n");
      }
    else
      {
      (void)dbfn_write(dbm_file, address_key, &new_address_record,
        (int)sizeof(dbdata_callout_cache_address));
      HDEBUG(D_verify) debug_printf("wrote %s callout cache address record\n",
        (new_address_record.result == ccache_accept)? "positive" : "negative");
      }
    }
  }    /* done */

/* 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. */

else   /* !done */
  {
  uschar *dullmsg = string_sprintf("Could not complete %s verify callout",
    is_recipient? "recipient" : "sender");
  yield = DEFER;

  if (host_list->next != NULL || addr->message == NULL) addr->message = dullmsg;

  addr->user_message = (!smtp_return_error_details)? dullmsg :
    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,
      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.");

  /* Force a specific error code */

  addr->basic_errno = ERRNO_CALLOUTDEFER;
  }

/* Come here from within the cache-reading code on fast-track exit. */

END_CALLOUT:
if (dbm_file != NULL) dbfn_close(dbm_file);
return yield;
}



/*************************************************
*           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;
  }
return yield;
}




/*************************************************
*            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

                     These ones are used by do_callout() -- the options variable
                       is passed to it.

                     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 *f, int options, int callout,
  int callout_overall, int callout_connect, uschar *se_mailfrom, 
  uschar *pm_mailfrom, BOOL *routed)
{
BOOL allok = TRUE;
BOOL full_info = (f == NULL)? FALSE : (debug_selector != 0);
BOOL is_recipient = (options & vopt_is_recipient) != 0;
BOOL expn         = (options & vopt_expn) != 0;
int i;
int yield = OK;
int verify_type = expn? v_expn :
     address_test_mode? v_none :
          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 = 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) == 0)
    {
    if (f != NULL)
      fprintf(f, "%sA domain is required for \"%s\"%s\n", ko_prefix, address,
        cr);
    *failure_ptr = US"qualify";     
    return FAIL;
    }
  address = rewrite_address_qualify(address, is_recipient);
  }

DEBUG(D_verify)
  {
  debug_printf(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n");
  debug_printf("%s %s\n", 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 != NULL)
  {
  uschar *old = address;
  address = rewrite_address(address, 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 (f != NULL && !expn) fprintf(f, "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)) == 0)
  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] == 0) return OK;

/* 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;

/* 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 != NULL)
  {
  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 (f != NULL)
      {
      BOOL allow;

      if (addr->address[0] == '>')
        {
        allow = testflag(addr, af_allow_reply);
        fprintf(f, "%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(f, "%s -> %s", addr->parent->address, addr->address);
        }

      if (addr->basic_errno == ERRNO_BADTRANSPORT)
        fprintf(f, "\n*** Error in setting up pipe, file, or autoreply:\n"
          "%s\n", addr->message);
      else if (allow)
        fprintf(f, "\n  transport = %s\n", addr->transport->name);
      else
        fprintf(f, " *** forbidden ***\n");
      }
    continue;
    }

  /* Just in case some router parameter refers to it. */

  return_path = (addr->p.errors_address != NULL)?
    addr->p.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 != NULL) *routed = FALSE;
  if ((rc = deliver_split_address(addr)) == OK)
    {
    if (!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 != NULL) *routed = TRUE;
    if (callout > 0)
      {
      host_item *host_list = addr->host_list;

      /* Default, if no remote transport, to NULL for the interface (=> any),
      "smtp" for the port, and "smtp" for the protocol. */

      transport_feedback tf = { NULL, US"smtp", US"smtp", NULL, FALSE, 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 (addr->transport != NULL && !addr->transport->info->local)
        {
        (void)(addr->transport->setup)(addr->transport, addr, &tf, 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 != NULL && (host_list == NULL || tf.hosts_override))
          {
          uschar *s;

          host_list = NULL;    /* Ignore the router's hosts */

          deliver_domain = addr->domain;
          deliver_localpart = addr->local_part;
          s = expand_string(tf.hosts);
          deliver_domain = deliver_localpart = NULL;

          if (s == NULL)
            {
            log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand list of hosts "
              "\"%s\" in %s transport for callout: %s", tf.hosts,
              addr->transport->name, expand_string_message);
            }
          else
            {
            uschar *canonical_name;
            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. */

            for (host = host_list; host != NULL; host = nexthost)
              {
              nexthost = host->next;
              if (tf.gethostbyname || string_is_ip_address(host->name, NULL))
                (void)host_find_byname(host, NULL, &canonical_name, TRUE);
              else
                {
                int flags = HOST_FIND_BY_A;
                if (tf.qualify_single) flags |= HOST_FIND_QUALIFY_SINGLE;
                if (tf.search_parents) flags |= HOST_FIND_SEARCH_PARENTS;
                (void)host_find_bydns(host, NULL, flags, NULL, NULL, NULL,
                  &canonical_name, 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 != NULL)
        {
        HDEBUG(D_verify) debug_printf("Attempting full verification using callout\n");
        if (host_checking && !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
          {
          rc = do_callout(addr, host_list, &tf, callout, callout_overall,
            callout_connect, options, se_mailfrom, pm_mailfrom);
          }
        }
      else
        {
        HDEBUG(D_verify) debug_printf("Cannot do callout: neither router nor "
          "transport provided a host list\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 (f != NULL)
      {
      fprintf(f, "%s%s %s", ko_prefix, address,
        address_test_mode? "is undeliverable" : "failed to verify");
      if (!expn && admin_user)
        {
        if (addr->basic_errno > 0)
          fprintf(f, ": %s", strerror(addr->basic_errno));
        if (addr->message != NULL)
          fprintf(f, ":\n  %s", addr->message);
        }
      fprintf(f, "%s\n", cr);
      }

    if (!full_info) return copy_error(vaddr, addr, FAIL);
      else yield = FAIL;
    }

  /* Soft failure */

  else if (rc == DEFER)
    {
    allok = FALSE;
    if (f != NULL)
      {
      fprintf(f, "%s%s cannot be resolved at this time", ko_prefix, address);
      if (!expn && admin_user)
        {
        if (addr->basic_errno > 0)
          fprintf(f, ":\n  %s", strerror(addr->basic_errno));
        if (addr->message != NULL)
          fprintf(f, ":\n  %s", addr->message);
        else if (addr->basic_errno <= 0)
          fprintf(f, ":\n  unknown error");
        }

      fprintf(f, "%s\n", cr);
      }
    if (!full_info) return copy_error(vaddr, addr, DEFER);
      else if (yield == OK) yield = DEFER;
    }

  /* If we are handling EXPN, we do not want to continue to route beyond
  the top level. */

  else if (expn)
    {
    uschar *ok_prefix = US"250-";
    if (addr_new == NULL)
      {
      if (addr_local == NULL && addr_remote == NULL)
        fprintf(f, "250 mail to <%s> is discarded\r\n", address);
      else
        fprintf(f, "250 <%s>\r\n", address);
      }
    else while (addr_new != NULL)
      {
      address_item *addr2 = addr_new;
      addr_new = addr2->next;
      if (addr_new == NULL) ok_prefix = US"250 ";
      fprintf(f, "%s<%s>\r\n", ok_prefix, addr2->address);
      }
    return OK;
    }

  /* 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 == NULL ||            /* No new address OR */
          addr_new->next != NULL ||      /* More than one new address OR */
          testflag(addr_new, af_pfr)))   /* New address is pfr */
      {
      if (f != NULL) fprintf(f, "%s %s\n", address,
        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->p.address_data = addr->p.address_data;
      return OK;
      }
    }
  }     /* 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 f 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 == NULL && addr_remote == NULL)
  fprintf(f, "mail to %s is discarded\n", address);

else for (addr_list = addr_local, i = 0; i < 2; addr_list = addr_remote, i++)
  {
  while (addr_list != NULL)
    {
    address_item *addr = addr_list;
    address_item *p = addr->parent;
    addr_list = addr->next;

    fprintf(f, "%s", CS addr->address);
    while (p != NULL)
      {
      fprintf(f, "\n    <-- %s", p->address);
      p = p->parent;
      }
    fprintf(f, "\n  ");

    /* Show router, and transport */

    fprintf(f, "router = %s, ", addr->router->name);
    fprintf(f, "transport = %s\n", (addr->transport == NULL)? US"unset" :
      addr->transport->name);

    /* 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 != NULL && addr->transport != NULL &&
        !addr->transport->overrides_hosts)
      {
      host_item *h;
      int maxlen = 0;
      int maxaddlen = 0;
      for (h = addr->host_list; h != NULL; h = h->next)
        {
        int len = Ustrlen(h->name);
        if (len > maxlen) maxlen = len;
        len = (h->address != NULL)? Ustrlen(h->address) : 7;
        if (len > maxaddlen) maxaddlen = len;
        }
      for (h = addr->host_list; h != NULL; h = h->next)
        {
        int len = Ustrlen(h->name);
        fprintf(f, "  host %s ", h->name);
        while (len++ < maxlen) fprintf(f, " ");
        if (h->address != NULL)
          {
          fprintf(f, "[%s] ", h->address);
          len = Ustrlen(h->address);
          }
        else if (!addr->transport->info->local)  /* Omit [unknown] for local */
          {
          fprintf(f, "[unknown] ");
          len = 7;
          }
        else len = -3;
        while (len++ < maxaddlen) fprintf(f," ");
        if (h->mx >= 0) fprintf(f, "MX=%d", h->mx);
        if (h->port != PORT_NONE) fprintf(f, " port=%d", h->port);
        if (h->status == hstatus_unusable) fprintf(f, " ** unusable **");
        fprintf(f, "\n");
        }
      }
    }
  }

/* Will be DEFER or FAIL if any one address has, only for full_info (which is 
the -bv or -bt case). */

return yield;  
}




/*************************************************
*      Check headers for syntax errors           *
*************************************************/

/* This function checks those header lines that contain addresses, and verifies
that all the addresses therein are 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;

for (h = header_list; h != NULL; 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++;

  parse_allow_group = TRUE;     /* Allow group syntax */

  /* Loop for multiple addresses in the header */

  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. */

    *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 != NULL && domain == 0)
      {
      if (h->type == htype_from || h->type == htype_sender)
        {
        if (!allow_unqualified_sender) recipient = NULL;
        }
      else
        {
        if (!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 == NULL && Ustrcmp(errmess, "empty address") != 0)
      {
      uschar *verb = US"is";
      uschar *t = ss;
      int len;

      /* Arrange not to include any white space at the end in the
      error message. */

      while (t > s && isspace(t[-1])) t--;

      /* Add the address which 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";
        }

      *msgptr = string_printing(
        string_sprintf("%s: failing address in \"%.*s\" header %s: %.*s",
          errmess, colon - h->text, h->text, verb, len, s));

      return FAIL;
      }

    /* Advance to the next address */

    s = ss + (terminator? 1:0);
    while (isspace(*s)) s++;
    }   /* Next address */
  }     /* Next header */

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())

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)
{
static int header_types[] = { htype_sender, htype_reply_to, htype_from };
int yield = FAIL;
int i;

for (i = 0; i < 3; i++)
  {
  header_line *h;
  for (h = header_list; h != NULL; h = h->next)
    {
    int terminator, new_ok;
    uschar *s, *ss, *endname;

    if (h->type != header_types[i]) continue;
    s = endname = Ustrchr(h->text, ':') + 1;

    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 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;
          if (*log_msgptr != NULL)
            {
            while (ss > s && isspace(ss[-1])) ss--;
            *log_msgptr = string_sprintf("syntax error in '%.*s' header when "
              "scanning for sender: %s in \"%.*s\"",
              endname - h->text, h->text, *log_msgptr, ss - s, s);
            return FAIL;
            }
          }

        /* Else go ahead with the sender verification. But is 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 && smtp_return_error_details)
        {
        *user_msgptr = string_sprintf("Rejected after DATA: "
          "could not verify \"%.*s\" header address\n%s: %s",
          endname - h->text, h->text, vaddr->address, vaddr->message);
        }

      /* Success or defer */

      if (new_ok == OK) return OK;
      if (new_ok == DEFER) yield = DEFER;

      /* Move on to any more addresses in the header */

      s = ss;
      }
    }
  }

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)
{
int sock, host_af, qlen;
int received_sender_port, received_interface_port, n;
uschar *p;
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;
sock = ip_socket(SOCK_STREAM, host_af);
if (sock < 0) return;

if (ip_bind(sock, host_af, interface_address, 0) < 0)
  {
  DEBUG(D_ident) debug_printf("bind socket for ident failed: %s\n",
    strerror(errno));
  goto END_OFF;
  }

if (ip_connect(sock, host_af, sender_host_address, port, rfc1413_query_timeout)
     < 0)
  {
  if (errno == ETIMEDOUT && (log_extra_selector & LX_ident_timeout) != 0)
    {
    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;
  }

/* Construct and send the query. */

sprintf(CS buffer, "%d , %d\r\n", sender_host_port, interface_port);
qlen = Ustrlen(buffer);
if (send(sock, buffer, qlen, 0) < 0)
  {
  DEBUG(D_ident) debug_printf("ident send failed: %s\n", 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(sock, 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. */

sender_ident = string_printing(string_copyn(p, 127));
DEBUG(D_ident) debug_printf("sender_ident = %s\n", sender_ident);

END_OFF:
close(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      the host name or NULL, implying use sender_host_name and
                   sender_host_aliases, looking them up if required
  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   failed to find the host name or IP address
                         unknown lookup type specified
*/

static int
check_host(void *arg, uschar *ss, uschar **valueptr, uschar **error)
{
check_host_block *cb = (check_host_block *)arg;
int maskoffset;
BOOL isquery = FALSE;
uschar *semicolon, *t;
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;
if it's "@[]" match against the local host's IP addresses. */

if (*ss == '@')
  {
  if (ss[1] == 0) 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) comparision with the current IP address. */

if (string_is_ip_address(ss, &maskoffset))
  return (host_is_in_net(cb->host_address, ss, maskoffset)? OK : FAIL);

/* 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. 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 = Ustrchr(ss, ';')) != NULL)
  {
  int mlen = 0;
  for (t = ss + 3; isdigit(*t); t++) mlen = mlen * 10 + *t - '0';
  if (*t++ == '-')
    {
    int insize;
    int search_type;
    int incoming[4];
    void *handle;
    uschar *filename, *key, *result;
    uschar buffer[64];

    /* If no mask was supplied, set a negative value */

    if (mlen == 0 && t == ss+4) mlen = -1;

    /* 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
    a single-key lookup, the key is the current IP address, masked
    appropriately, and reconverted to text form, with the mask appended. */

    if (mac_islookup(search_type, lookup_querystyle))
      {
      filename = NULL;
      key = semicolon + 1;
      }
    else
      {
      insize = host_aton(cb->host_address, incoming);
      host_mask(insize, incoming, mlen);
      (void)host_nmtoa(insize, incoming, mlen, buffer);
      key = buffer;
      filename = semicolon + 1;
      }

    /* Now do the actual lookup; note that there is no search_close() because
    of the caching arrangements. */

    handle = search_open(filename, search_type, 0, NULL, NULL);
    if (handle == 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 != NULL) *valueptr = result;
    return (result != NULL)? OK : 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. 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;
  rc = host_find_byname(&h, NULL, NULL, FALSE);
  if (rc == HOST_FOUND || rc == HOST_FOUND_LOCAL)
    {
    host_item *hh;
    for (hh = &h; hh != NULL; hh = hh->next)
      {
      if (Ustrcmp(hh->address, (Ustrchr(hh->address, ':') == NULL)?
        cb->host_ipv4 : 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)
  {
  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);
  }

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 == NULL)
  {
  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 != NULL)
  {
  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(uschar **listptr, unsigned int *cache_bits,
  uschar *host_name, uschar *host_address, uschar **valueptr)
{
int rc;
unsigned int *local_cache_bits = cache_bits;
uschar *save_host_address = deliver_host_address;
check_host_block cb;
cb.host_name = host_name;
cb.host_address = host_address;

if (valueptr != NULL) *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 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(listptr, sender_host_cache, NULL,
  (sender_host_address == NULL)? US"" : sender_host_address, NULL);
}





/*************************************************
*    Invert an IP address for a DNS black list   *
*************************************************/

/*
Arguments:
  buffer         where to put the answer
  address        the address to invert
*/

static 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
}



/*************************************************
*        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.

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:
  listptr      the domain/address/data list

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(uschar **listptr)
{
int sep = 0;
int defer_return = FAIL;
int old_pool = store_pool;
BOOL invert_result = FALSE;
uschar *list = *listptr;
uschar *domain;
uschar *s;
uschar buffer[1024];
uschar query[256];         /* DNS domain max length */
uschar revadd[128];        /* Long enough for IPv6 address */

/* Indicate that the inverted IP address is not yet set up */

revadd[0] = 0;

/* Loop through all the domains supplied, until something matches */

while ((domain = string_nextinlist(&list, &sep, buffer, sizeof(buffer))) != NULL)
  {
  BOOL frc;
  BOOL bitmask = FALSE;
  dns_answer dnsa;
  dns_scan dnss;
  uschar *iplist;
  uschar *key;
  tree_node *t;
  dnsbl_cache_block *cb;

  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 */

  key = Ustrchr(domain, '/');
  if (key != NULL) *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 invert the result.
  */

  iplist = Ustrchr(domain, '=');
  if (iplist == NULL)
    {
    bitmask = TRUE;
    iplist = Ustrchr(domain, '&');
    }

  if (iplist != NULL)
    {
    if (iplist > domain && iplist[-1] == '!')
      {
      invert_result = TRUE;
      iplist[-1] = 0;
      }
    *iplist++ = 0;
    }

  /* 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 != '.')
      {
      log_write(0, LOG_MAIN, "dnslists domain \"%s\" contains "
        "strange characters - is this right?", domain);
      break;
      }
    }

  /* Construct the query by adding the domain onto either the sending host
  address, or the given key string. */

  if (key == NULL)
    {
    if (sender_host_address == NULL) return FAIL;    /* can never match */
    if (revadd[0] == 0) invert_address(revadd, sender_host_address);
    frc = string_format(query, sizeof(query), "%s%s", revadd, domain);
    }
  else
    {
    frc = string_format(query, sizeof(query), "%s.%s", key, domain);
    }

  if (!frc)
    {
    log_write(0, LOG_MAIN|LOG_PANIC, "dnslist query is too long "
      "(ignored): %s...", query);
    continue;
    }

  /* Look for this query in the cache. */

  t = tree_search(dnsbl_cache, query);

  /* If not cached from a previous lookup, we must do a DNS lookup, and
  cache the result in permanent memory. */

  if (t == NULL)
    {
    store_pool = POOL_PERM;

    /* In case this is the first time the DNS resolver is being used. */

    dns_init(FALSE, FALSE);

    /* 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 loopup . */

    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 have been reduced to experimental
    status (August 2001) and may die out. So they may never get used at all,
    let alone in dnsbl records. However, 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. */

    if (cb->rc == DNS_SUCCEED)
      {
      dns_record *rr;
      dns_address **addrp = &(cb->rhs);
      for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
           rr != NULL;
           rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
        {
        if (rr->type == T_A)
          {
          dns_address *da = dns_address_from_rr(&dnsa, rr);
          if (da != NULL)
            {
            *addrp = da;
            while (da->next != NULL) da = da->next;
            addrp = &(da->next);
            }
          }
        }

      /* 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 == NULL) cb->rc = DNS_NODATA;
      }

    store_pool = old_pool;
    }

  /* Previous lookup was cached */

  else
    {
    HDEBUG(D_dnsbl) debug_printf("using result of previous DNS lookup\n");
    cb = t->data.ptr;
    }

  /* 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 != NULL; 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 != NULL)
      {
      int ipsep = ',';
      uschar ip[46];
      uschar *ptr = iplist;

      while (string_nextinlist(&ptr, &ipsep, ip, sizeof(ip)) != NULL)
        {
        /* Handle exact matching */
        if (!bitmask)
          {
          for (da = cb->rhs; da != NULL; da = da->next)
            {
            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(ip, address) == 1) mask = address[0];

          /* Scan the returned addresses, skipping any that are IPv6 */

          for (da = cb->rhs; da != NULL; da = da->next)
            {
            if (host_aton(da->address, address) != 1) continue;
            if ((address[0] & mask) == mask) break;
            }
          }

        /* Break out if a match has been found */

        if (da != NULL) break;
        }

      /* If either

         (a) No IP address in a positive list matched, or
         (b) An IP address in a negative list did match

      then behave as if the DNSBL lookup had not succeeded, i.e. the host is
      not on the list. */

      if (invert_result != (da == NULL))
        {
        HDEBUG(D_dnsbl)
          {
          debug_printf("=> but we are not accepting this block class because\n");
          debug_printf("=> there was %s match for %c%s\n",
            invert_result? "an exclude":"no", bitmask? '&' : '=', iplist);
          }
        continue;   /* With next DNSBL domain */
        }
      }

  /* Either there was no IP list, or the record matched. Look up a TXT record
    if it hasn't previously been done. */

    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 != NULL;
             rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
          if (rr->type == T_TXT) break;
        if (rr != NULL)
          {
          int len = (rr->data)[0];
          if (len > 511) len = 127;
          store_pool = POOL_PERM;
          cb->text = string_sprintf("%.*s", len, (const uschar *)(rr->data+1));
          store_pool = old_pool;
          }
        }
      }

    HDEBUG(D_dnsbl)
      {
      debug_printf("=> that means %s is listed at %s\n",
        (key == NULL)? sender_host_address : key, domain);
      }

    dnslist_domain = string_copy(domain);
    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",
      (key == NULL)? sender_host_address : key, domain);
    }
  }      /* Continue with next domain */

return FAIL;
}

/* End of verify.c */