Fix cutthrough delivery for more than one iteration of address redirection. Bug...
[exim.git] / src / src / verify.c
index 4af863c0bc80e7cf6fc7642ada24280551caef5b..6411899c80081e2b00acbb5876b205eabb7f7f94 100644 (file)
@@ -2,7 +2,7 @@
 *     Exim - an Internet mail transport agent    *
 *************************************************/
 
-/* Copyright (c) University of Cambridge 1995 - 2016 */
+/* Copyright (c) University of Cambridge 1995 - 2018 */
 /* See the file NOTICE for conditions of use and distribution. */
 
 /* Functions concerned with verifying things. The original code for callout
@@ -39,7 +39,7 @@ static tree_node *dnsbl_cache = NULL;
 #define MT_NOT 1
 #define MT_ALL 2
 
-static uschar cutthrough_response(char, uschar **, int);
+static uschar cutthrough_response(client_conn_ctx *, char, uschar **, int);
 
 
 
@@ -68,9 +68,7 @@ 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)
+if (!(cache_record = dbfn_read_with_length(dbm_file, key, &length)))
   {
   HDEBUG(D_verify) debug_printf("callout cache: no %s record found for %s\n", type, key);
   return NULL;
@@ -119,97 +117,21 @@ 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_fullpm => if postmaster check, do full one
-                      vopt_callout_random => do the "random" thing
-                      vopt_callout_recipsender => use real sender for recipient
-                      vopt_callout_recippmaster => use postmaster for recipient
-  se_mailfrom         MAIL FROM address for sender verify; NULL => ""
-  pm_mailfrom         if non-NULL, do the postmaster check with this sender
+/* Check the callout cache.
+Options * pm_mailfrom may be modified by cache partial results.
 
-Returns:            OK/FAIL/DEFER
+Return: TRUE if result found
 */
 
-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)
+static BOOL
+cached_callout_lookup(address_item * addr, uschar * address_key,
+  uschar * from_address, int * opt_ptr, uschar ** pm_ptr,
+  int * yield, uschar ** failure_ptr,
+  dbdata_callout_cache * new_domain_record, int * old_domain_res)
 {
-int yield = OK;
-int old_domain_cache_result = ccache_accept;
-BOOL done = FALSE;
-uschar *address_key;
-uschar *from_address;
-uschar *random_local_part = NULL;
-const uschar *save_deliver_domain = deliver_domain;
-uschar **failure_ptr = options & vopt_is_recipient
-  ? &recipient_verify_failure : &sender_verify_failure;
+int options = *opt_ptr;
 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 (options & vopt_is_recipient)
-  {
-  if (options & vopt_callout_recipsender)
-    {
-    address_key = string_sprintf("%s/<%s>", addr->address, sender_address);
-    from_address = sender_address;
-    if (cutthrough.delivery) options |= vopt_callout_no_cache;
-    }
-  else if (options & vopt_callout_recippmaster)
-    {
-    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. */
@@ -218,21 +140,19 @@ if (options & vopt_callout_no_cache)
   {
   HDEBUG(D_verify) debug_printf("callout cache: disabled by no_cache\n");
   }
-else if ((dbm_file = dbfn_open(US"callout", O_RDWR, &dbblock, FALSE)) == NULL)
+else if (!(dbm_file = dbfn_open(US"callout", O_RDWR, &dbblock, FALSE)))
   {
   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)
+else
   {
-  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 a cache database is available see if we can avoid the need to do an
+  actual callout by making use of previously-obtained data. */
+
+  dbdata_callout_cache_address * cache_address_record;
+  dbdata_callout_cache * cache_record = get_callout_cache_record(dbm_file,
+      addr->domain, US"domain",
+      callout_cache_domain_positive_expire, callout_cache_domain_negative_expire);
 
   /* If an unexpired cache record was found for this domain, see if the callout
   process can be short-circuited. */
@@ -247,20 +167,20 @@ if (dbm_file)
     not to disturb the cached domain value if this whole verification succeeds
     (we don't want it turning into "accept"). */
 
-    old_domain_cache_result = cache_record->result;
+    *old_domain_res = cache_record->result;
 
-    if (cache_record->result == ccache_reject ||
-         (*from_address == 0 && cache_record->result == ccache_reject_mfnull))
+    if (  cache_record->result == ccache_reject
+       || *from_address == 0 && cache_record->result == ccache_reject_mfnull)
       {
-      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");
+       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;
+      *yield = FAIL;
       *failure_ptr = US"mail";
-      goto END_CALLOUT;
+      dbfn_close(dbm_file);
+      return TRUE;
       }
 
     /* If a previous check on a "random" local part was accepted, we assume
@@ -275,21 +195,24 @@ if (dbm_file)
       case ccache_accept:
        HDEBUG(D_verify)
          debug_printf("callout cache: domain accepts random addresses\n");
-       goto END_CALLOUT;     /* Default yield is OK */
+       *failure_ptr = US"random";
+       dbfn_close(dbm_file);
+       return TRUE;     /* Default yield is OK */
 
       case ccache_reject:
        HDEBUG(D_verify)
          debug_printf("callout cache: domain rejects random addresses\n");
-       options &= ~vopt_callout_random;
-       new_domain_record.random_result = ccache_reject;
-       new_domain_record.random_stamp = cache_record->random_stamp;
+       *opt_ptr = options & ~vopt_callout_random;
+       new_domain_record->random_result = ccache_reject;
+       new_domain_record->random_stamp = cache_record->random_stamp;
        break;
 
       default:
        HDEBUG(D_verify)
          debug_printf("callout cache: need to check random address handling "
            "(not cached or cache expired)\n");
-       goto END_CACHE;
+       dbfn_close(dbm_file);
+       return FALSE;
       }
 
     /* If a postmaster check is requested, but there was a previous failure,
@@ -297,27 +220,29 @@ if (dbm_file)
     but has not been done before, we are going to have to do a callout, so skip
     remaining cache processing. */
 
-    if (pm_mailfrom)
+    if (*pm_ptr)
       {
       if (cache_record->postmaster_result == ccache_reject)
-        {
-        setflag(addr, af_verify_pmfail);
-        HDEBUG(D_verify)
-          debug_printf("callout cache: domain does not accept "
-            "RCPT TO:<postmaster@domain>\n");
-        yield = FAIL;
-        *failure_ptr = US"postmaster";
-        setflag(addr, af_verify_pmfail);
-        addr->user_message = US"(result of earlier verification reused).";
-        goto END_CALLOUT;
-        }
+       {
+       setflag(addr, af_verify_pmfail);
+       HDEBUG(D_verify)
+         debug_printf("callout cache: domain does not accept "
+           "RCPT TO:<postmaster@domain>\n");
+       *yield = FAIL;
+       *failure_ptr = US"postmaster";
+       setflag(addr, af_verify_pmfail);
+       addr->user_message = US"(result of earlier verification reused).";
+       dbfn_close(dbm_file);
+       return TRUE;
+       }
       if (cache_record->postmaster_result == ccache_unknown)
-        {
-        HDEBUG(D_verify)
-          debug_printf("callout cache: need to check RCPT "
-            "TO:<postmaster@domain> (not cached or cache expired)\n");
-        goto END_CACHE;
-        }
+       {
+       HDEBUG(D_verify)
+         debug_printf("callout cache: need to check RCPT "
+           "TO:<postmaster@domain> (not cached or cache expired)\n");
+       dbfn_close(dbm_file);
+       return FALSE;
+       }
 
       /* If cache says OK, set pm_mailfrom NULL to prevent a redundant
       postmaster check if the address itself has to be checked. Also ensure
@@ -325,10 +250,10 @@ if (dbm_file)
       */
 
       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;
+       "TO:<postmaster@domain>\n");
+      *pm_ptr = NULL;
+      new_domain_record->postmaster_result = ccache_accept;
+      new_domain_record->postmaster_stamp = cache_record->postmaster_stamp;
       }
     }
 
@@ -337,35 +262,306 @@ if (dbm_file)
   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 = (dbdata_callout_cache_address *)
+    get_callout_cache_record(dbm_file, address_key, US"address",
+      callout_cache_positive_expire, callout_cache_negative_expire)))
+    {
+    dbfn_close(dbm_file);
+    return FALSE;
+    }
 
-  if (cache_address_record)
+  if (cache_address_record->result == ccache_accept)
     {
-    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;
+    HDEBUG(D_verify)
+      debug_printf("callout cache: address record is positive\n");
+    }
+  else
+    {
+    HDEBUG(D_verify)
+      debug_printf("callout cache: address record is negative\n");
+    addr->user_message = US"Previous (cached) callout verification failure";
+    *failure_ptr = US"recipient";
+    *yield = FAIL;
     }
 
   /* Close the cache database while we actually do the callout for real. */
 
-  END_CACHE:
   dbfn_close(dbm_file);
-  dbm_file = NULL;
+  return TRUE;
+  }
+return FALSE;
+}
+
+
+/* Write results to callout cache
+*/
+static void
+cache_callout_write(dbdata_callout_cache * dom_rec, const uschar * domain,
+  int done, dbdata_callout_cache_address * addr_rec, uschar * address_key)
+{
+open_db dbblock;
+open_db *dbm_file = NULL;
+
+/* If we get here with done == TRUE, a successful callout happened, and yield
+will be set OK or FAIL according to the response to the RCPT command.
+Otherwise, we looped through the hosts but couldn't complete the business.
+However, there may be domain-specific information to cache in both cases.
+
+The value of the result field in the new_domain record is ccache_unknown if
+there was an error before or with MAIL FROM:, and errno was not zero,
+implying some kind of I/O error. We don't want to write the cache in that case.
+Otherwise the value is ccache_accept, ccache_reject, or ccache_reject_mfnull. */
+
+if (dom_rec->result != ccache_unknown)
+  if (!(dbm_file = dbfn_open(US"callout", O_RDWR|O_CREAT, &dbblock, FALSE)))
+    {
+    HDEBUG(D_verify) debug_printf("callout cache: not available\n");
+    }
+  else
+    {
+    (void)dbfn_write(dbm_file, domain, dom_rec,
+      (int)sizeof(dbdata_callout_cache));
+    HDEBUG(D_verify) debug_printf("wrote callout cache domain record for %s:\n"
+      "  result=%d postmaster=%d random=%d\n",
+      domain,
+      dom_rec->result,
+      dom_rec->postmaster_result,
+      dom_rec->random_result);
+    }
+
+/* If a definite result was obtained for the callout, cache it unless caching
+is disabled. */
+
+if (done  &&  addr_rec->result != ccache_unknown)
+  {
+  if (!dbm_file)
+    dbm_file = dbfn_open(US"callout", O_RDWR|O_CREAT, &dbblock, FALSE);
+  if (!dbm_file)
+    {
+    HDEBUG(D_verify) debug_printf("no callout cache available\n");
+    }
+  else
+    {
+    (void)dbfn_write(dbm_file, address_key, addr_rec,
+      (int)sizeof(dbdata_callout_cache_address));
+    HDEBUG(D_verify) debug_printf("wrote %s callout cache address record for %s\n",
+      addr_rec->result == ccache_accept ? "positive" : "negative",
+      address_key);
+    }
+  }
+
+if (dbm_file) dbfn_close(dbm_file);
+}
+
+
+/* Cutthrough-multi.  If the existing cached cutthrough connection matches
+the one we would make for a subsequent recipient, use it.  Send the RCPT TO
+and check the result, nonpipelined as it may be wanted immediately for
+recipient-verification.
+
+It seems simpler to deal with this case separately from the main callout loop.
+We will need to remember it has sent, or not, so that rcpt-acl tail code
+can do it there for the non-rcpt-verify case.  For this we keep an addresscount.
+
+Return: TRUE for a definitive result for the recipient
+*/
+static int
+cutthrough_multi(address_item * addr, host_item * host_list,
+  transport_feedback * tf, int * yield)
+{
+BOOL done = FALSE;
+host_item * host;
+
+if (addr->transport == cutthrough.addr.transport)
+  for (host = host_list; host; host = host->next)
+    if (Ustrcmp(host->address, cutthrough.host.address) == 0)
+      {
+      int host_af;
+      uschar *interface = NULL;  /* Outgoing interface to use; NULL => any */
+      int port = 25;
+
+      deliver_host = host->name;
+      deliver_host_address = host->address;
+      deliver_host_port = host->port;
+      deliver_domain = addr->domain;
+      transport_name = addr->transport->name;
+
+      host_af = Ustrchr(host->address, ':') ? AF_INET6 : AF_INET;
+
+      if (  !smtp_get_interface(tf->interface, host_af, addr, &interface,
+             US"callout")
+        || !smtp_get_port(tf->port, addr, &port, US"callout")
+        )
+       log_write(0, LOG_MAIN|LOG_PANIC, "<%s>: %s", addr->address,
+         addr->message);
+
+      smtp_port_for_connect(host, port);
+
+      if (  (  interface == cutthrough.interface
+           || (  interface
+              && cutthrough.interface
+              && Ustrcmp(interface, cutthrough.interface) == 0
+           )  )
+        && host->port == cutthrough.host.port
+        )
+       {
+       uschar * resp = NULL;
+
+       /* Match!  Send the RCPT TO, set done from the response */
+       done =
+            smtp_write_command(&ctblock, SCMD_FLUSH, "RCPT TO:<%.1000s>\r\n",
+             transport_rcpt_address(addr,
+                addr->transport->rcpt_include_affixes)) >= 0
+         && cutthrough_response(&cutthrough.cctx, '2', &resp,
+             CUTTHROUGH_DATA_TIMEOUT) == '2';
+
+       /* This would go horribly wrong if a callout fail was ignored by ACL.
+       We punt by abandoning cutthrough on a reject, like the
+       first-rcpt does. */
+
+       if (done)
+         {
+         address_item * na = store_get(sizeof(address_item));
+         *na = cutthrough.addr;
+         cutthrough.addr = *addr;
+         cutthrough.addr.host_used = &cutthrough.host;
+         cutthrough.addr.next = na;
+
+         cutthrough.nrcpt++;
+         }
+       else
+         {
+         cancel_cutthrough_connection(TRUE, US"recipient rejected");
+         if (!resp || errno == ETIMEDOUT)
+           {
+           HDEBUG(D_verify) debug_printf("SMTP timeout\n");
+           }
+         else if (errno == 0)
+           {
+           if (*resp == 0)
+             Ustrcpy(resp, US"connection dropped");
+
+           addr->message =
+             string_sprintf("response to \"%s\" was: %s",
+               big_buffer, string_printing(resp));
+
+           addr->user_message =
+             string_sprintf("Callout verification failed:\n%s", resp);
+
+           /* Hard rejection ends the process */
+
+           if (resp[0] == '5')   /* Address rejected */
+             {
+             *yield = FAIL;
+             done = TRUE;
+             }
+           }
+         }
+       }
+      break;   /* host_list */
+      }
+if (!done)
+  cancel_cutthrough_connection(TRUE, US"incompatible connection");
+return done;
+}
+
+
+/*************************************************
+*      Do callout verification for an address    *
+*************************************************/
+
+/* This function is called from verify_address() when the address has routed to
+a host list, and a callout has been requested. Callouts are expensive; that is
+why a cache is used to improve the efficiency.
+
+Arguments:
+  addr              the address that's been routed
+  host_list         the list of hosts to try
+  tf                the transport feedback block
+
+  ifstring          "interface" option from transport, or NULL
+  portstring        "port" option from transport, or NULL
+  protocolstring    "protocol" option from transport, or NULL
+  callout           the per-command callout timeout
+  callout_overall   the overall callout timeout (if < 0 use 4*callout)
+  callout_connect   the callout connection timeout (if < 0 use callout)
+  options           the verification options - these bits are used:
+                      vopt_is_recipient => this is a recipient address
+                      vopt_callout_no_cache => don't use callout cache
+                      vopt_callout_fullpm => if postmaster check, do full one
+                      vopt_callout_random => do the "random" thing
+                      vopt_callout_recipsender => use real sender for recipient
+                      vopt_callout_recippmaster => use postmaster for recipient
+                     vopt_callout_hold         => lazy close connection
+  se_mailfrom         MAIL FROM address for sender verify; NULL => ""
+  pm_mailfrom         if non-NULL, do the postmaster check with this sender
+
+Returns:            OK/FAIL/DEFER
+*/
+
+static int
+do_callout(address_item *addr, host_item *host_list, transport_feedback *tf,
+  int callout, int callout_overall, int callout_connect, int options,
+  uschar *se_mailfrom, uschar *pm_mailfrom)
+{
+int yield = OK;
+int old_domain_cache_result = ccache_accept;
+BOOL done = FALSE;
+uschar *address_key;
+uschar *from_address;
+uschar *random_local_part = NULL;
+const uschar *save_deliver_domain = deliver_domain;
+uschar **failure_ptr = options & vopt_is_recipient
+  ? &recipient_verify_failure : &sender_verify_failure;
+dbdata_callout_cache new_domain_record;
+dbdata_callout_cache_address new_address_record;
+time_t callout_start_time;
+
+new_domain_record.result = ccache_unknown;
+new_domain_record.postmaster_result = ccache_unknown;
+new_domain_record.random_result = ccache_unknown;
+
+memset(&new_address_record, 0, sizeof(new_address_record));
+
+/* For a recipient callout, the key used for the address cache record must
+include the sender address if we are using the real sender in the callout,
+because that may influence the result of the callout. */
+
+if (options & vopt_is_recipient)
+  if (options & vopt_callout_recipsender)
+    {
+    from_address = sender_address;
+    address_key = string_sprintf("%s/<%s>", addr->address, sender_address);
+    if (cutthrough.delivery) options |= vopt_callout_no_cache;
+    }
+  else if (options & vopt_callout_recippmaster)
+    {
+    from_address = string_sprintf("postmaster@%s", qualify_domain_sender);
+    address_key = string_sprintf("%s/<postmaster@%s>", addr->address,
+      qualify_domain_sender);
+    }
+  else
+    {
+    from_address = US"";
+    address_key = addr->address;
+    }
+
+/* For a sender callout, we must adjust the key if the mailfrom address is not
+empty. */
+
+else
+  {
+  from_address = se_mailfrom ? se_mailfrom : US"";
+  address_key = *from_address
+    ? string_sprintf("%s/<%s>", addr->address, from_address) : addr->address;
+  }
+
+if (cached_callout_lookup(addr, address_key, from_address,
+      &options, &pm_mailfrom, &yield, failure_ptr,
+      &new_domain_record, &old_domain_cache_result))
+  {
+  cancel_cutthrough_connection(TRUE, US"cache-hit");
+  goto END_CALLOUT;
   }
 
 if (!addr->transport)
@@ -379,6 +575,7 @@ else
   {
   smtp_transport_options_block *ob =
     (smtp_transport_options_block *)addr->transport->options_block;
+  host_item * host;
 
   /* The information wasn't available in the cache, so we have to do a real
   callout and save the result in the cache for next time, unless no_cache is set,
@@ -386,7 +583,7 @@ else
   with a random local part, ensure that such a local part is available. If not,
   log the fact, but carry on without randomising. */
 
-  if (options & vopt_callout_random && callout_random_local_part != NULL)
+  if (options & vopt_callout_random  &&  callout_random_local_part)
     if (!(random_local_part = expand_string(callout_random_local_part)))
       log_write(0, LOG_MAIN|LOG_PANIC, "failed to expand "
         "callout_random_local_part: %s", expand_string_message);
@@ -406,115 +603,25 @@ else
 
   if (smtp_out && !disable_callout_flush) mac_smtp_fflush();
 
+  clearflag(addr, af_verify_pmfail);  /* postmaster callout flag */
+  clearflag(addr, af_verify_nsfail);  /* null sender callout flag */
+
 /* cutthrough-multi: if a nonfirst rcpt has the same routing as the first,
 and we are holding a cutthrough conn open, we can just append the rcpt to
 that conn for verification purposes (and later delivery also).  Simplest
-coding means skipping this whole loop and doing the append separately.
-
-We will need to remember it has been appended so that rcpt-acl tail code
-can do it there for the non-rcpt-verify case.  For this we keep an addresscount.
-*/
+coding means skipping this whole loop and doing the append separately.  */
 
   /* Can we re-use an open cutthrough connection? */
-  if (  cutthrough.fd >= 0
+  if (  cutthrough.cctx.sock >= 0
      && (options & (vopt_callout_recipsender | vopt_callout_recippmaster))
        == vopt_callout_recipsender
      && !random_local_part
      && !pm_mailfrom
      )
-    {
-    if (addr->transport == cutthrough.addr.transport)
-      for (host = host_list; host; host = host->next)
-       if (Ustrcmp(host->address, cutthrough.host.address) == 0)
-         {
-         int host_af;
-         uschar *interface = NULL;  /* Outgoing interface to use; NULL => any */
-         int port = 25;
-
-         deliver_host = host->name;
-         deliver_host_address = host->address;
-         deliver_host_port = host->port;
-         deliver_domain = addr->domain;
-         transport_name = addr->transport->name;
-
-         host_af = (Ustrchr(host->address, ':') == NULL)? AF_INET:AF_INET6;
-
-         if (!smtp_get_interface(tf->interface, host_af, addr, &interface,
-                 US"callout") ||
-             !smtp_get_port(tf->port, addr, &port, US"callout"))
-           log_write(0, LOG_MAIN|LOG_PANIC, "<%s>: %s", addr->address,
-             addr->message);
-
-         if (  (  interface == cutthrough.interface
-               || (  interface
-                  && cutthrough.interface
-                  && Ustrcmp(interface, cutthrough.interface) == 0
-               )  )
-            && port == cutthrough.host.port
-            )
-           {
-           uschar * resp = NULL;
-
-           /* Match!  Send the RCPT TO, append the addr, set done */
-           done =
-             smtp_write_command(&ctblock, FALSE, "RCPT TO:<%.1000s>\r\n",
-               transport_rcpt_address(addr,
-                 (addr->transport == NULL)? FALSE :
-                  addr->transport->rcpt_include_affixes)) >= 0 &&
-             cutthrough_response('2', &resp, CUTTHROUGH_DATA_TIMEOUT) == '2';
+    done = cutthrough_multi(addr, host_list, tf, &yield);
 
-           /* This would go horribly wrong if a callout fail was ignored by ACL.
-           We punt by abandoning cutthrough on a reject, like the
-           first-rcpt does. */
-
-           if (done)
-             {
-             address_item * na = store_get(sizeof(address_item));
-             *na = cutthrough.addr;
-             cutthrough.addr = *addr;
-             cutthrough.addr.host_used = &cutthrough.host;
-             cutthrough.addr.next = na;
-
-             cutthrough.nrcpt++;
-             }
-           else
-             {
-             cancel_cutthrough_connection("recipient rejected");
-             if (!resp || errno == ETIMEDOUT)
-               {
-               HDEBUG(D_verify) debug_printf("SMTP timeout\n");
-               }
-             else if (errno == 0)
-               {
-               if (*resp == 0)
-                 Ustrcpy(resp, US"connection dropped");
-
-               addr->message =
-                 string_sprintf("response to \"%s\" from %s [%s] was: %s",
-                   big_buffer, host->name, host->address,
-                   string_printing(resp));
-
-               addr->user_message =
-                 string_sprintf("Callout verification failed:\n%s", resp);
-
-               /* Hard rejection ends the process */
-
-               if (resp[0] == '5')   /* Address rejected */
-                 {
-                 yield = FAIL;
-                 done = TRUE;
-                 }
-               }
-             }
-           }
-         break;        /* host_list */
-         }
-    if (!done)
-      cancel_cutthrough_connection("incompatible connection");
-    }
-
-  /* Now make connections to the hosts and do real callouts. The list of hosts
-  is passed in as an argument. */
+  /* If we did not use a cached connection, make connections to the hosts
+  and do real callouts. The list of hosts is passed in as an argument. */
 
   for (host = host_list; host && !done; host = host->next)
     {
@@ -522,12 +629,6 @@ can do it there for the non-rcpt-verify case.  For this we keep an addresscount.
     int port = 25;
     uschar *interface = NULL;  /* Outgoing interface to use; NULL => any */
     smtp_context sx;
-    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)
       {
@@ -546,7 +647,7 @@ can do it there for the non-rcpt-verify case.  For this we keep an addresscount.
 
     /* Set IPv4 or IPv6 */
 
-    host_af = Ustrchr(host->address, ':') == NULL ? AF_INET : AF_INET6;
+    host_af = Ustrchr(host->address, ':') ? AF_INET6 : AF_INET;
 
     /* Expand and interpret the interface and port strings. The latter will not
     be used if there is a host-specific port (e.g. from a manualroute router).
@@ -574,6 +675,7 @@ can do it there for the non-rcpt-verify case.  For this we keep an addresscount.
     sx.interface = interface;
     sx.helo_data = tf->helo_data;
     sx.tblock = addr->transport;
+    sx.verify = TRUE;
 
 tls_retry_connection:
     /* Set the address state so that errors are recorded in it */
@@ -586,21 +688,23 @@ tls_retry_connection:
     SMTP command to send.  If we tried TLS but it failed, try again without
     if permitted */
 
-    if (  (yield = smtp_setup_conn(&sx, FALSE, TRUE)) == DEFER
+    yield = smtp_setup_conn(&sx, FALSE);
+#ifdef SUPPORT_TLS
+    if (  yield == DEFER
        && addr->basic_errno == ERRNO_TLSFAILURE
        && ob->tls_tempfail_tryclear
        && verify_check_given_host(&ob->hosts_require_tls, host) != OK
        )
       {
-      log_write(0, LOG_MAIN, "TLS session failure:"
-       " callout unencrypted to %s [%s] (not in hosts_require_tls)",
-       host->name, host->address);
-      yield = smtp_setup_conn(&sx, TRUE, TRUE);
+      log_write(0, LOG_MAIN,
+       "%s: callout unencrypted to %s [%s] (not in hosts_require_tls)",
+       addr->message, host->name, host->address);
+      addr->transport_return = PENDING_DEFER;
+      yield = smtp_setup_conn(&sx, TRUE);
       }
+#endif
     if (yield != OK)
       {
-      if (addr->message) addr->message = string_sprintf("%s [%s] %s",
-                                     host->name, host->address, addr->message);
       errno = addr->basic_errno;
       transport_name = NULL;
       deliver_host = deliver_host_address = NULL;
@@ -626,66 +730,21 @@ tls_retry_connection:
     addr->authenticator = client_authenticator;
     addr->auth_id = client_authenticated_id;
 
-    /* Build a mail-AUTH string (re-using responsebuffer for convenience */
-
-    done =
-        !smtp_mail_auth_str(responsebuffer, sizeof(responsebuffer), addr, ob)
-      && (
-         (addr->auth_sndr = client_authenticated_sender),
-
-    /* Send the MAIL command */
-
-         (smtp_write_command(&sx.outblock, FALSE,
-#ifdef SUPPORT_I18N
-           addr->prop.utf8_msg && !addr->prop.utf8_downcvt
-           ? "MAIL FROM:<%s>%s%s SMTPUTF8\r\n"
-           :
-#endif
-             "MAIL FROM:<%s>%s%s\r\n",
-           from_address,
-           responsebuffer,
-           options & vopt_is_recipient && sx.peer_offered & PEER_OFFERED_SIZE
-           ? string_sprintf(" SIZE=%d", message_size + ob->size_addition)
-           : US""
-
-           ) >= 0)
-        )
-
-      && smtp_read_response(&sx.inblock, responsebuffer, sizeof(responsebuffer),
-         '2', callout);
+    sx.from_addr = from_address;
+    sx.first_addr = sx.sync_addr = addr;
+    sx.ok = FALSE;                     /*XXX these 3 last might not be needed for verify? */
+    sx.send_rset = TRUE;
+    sx.completed_addr = FALSE;
 
-    deliver_host = deliver_host_address = NULL;
-    deliver_domain = save_deliver_domain;
+    new_domain_record.result = old_domain_cache_result == ccache_reject_mfnull
+      ? ccache_reject_mfnull : ccache_accept;
 
-    /* If the host does not accept MAIL FROM:<>, arrange to cache this
-    information, but again, don't record anything for an I/O error or a defer. Do
-    not cache rejections of MAIL when a non-empty sender has been used, because
-    that blocks the whole domain for all senders. */
+    /* Do the random local part check first. Temporarily replace the recipient
+    with the "random" value */
 
-    if (!done)
-      {
-      *failure_ptr = US"mail";     /* At or before MAIL */
-      if (errno == 0 && responsebuffer[0] == '5')
-        {
-        setflag(addr, af_verify_nsfail);
-        if (from_address[0] == 0)
-          new_domain_record.result = ccache_reject_mfnull;
-        }
-      }
-
-    /* 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:<>.
-
-    Before doing this, set the result in the domain cache record to "accept",
-    unless its previous value was ccache_reject_mfnull. In that case, the domain
-    rejects MAIL FROM:<> and we want to continue to remember that. When that is
-    the case, we have got here only in the case of a recipient verification with
-    a non-null sender. */
-
-    else
+    if (random_local_part)
       {
+      uschar * main_address = addr->address;
       const uschar * rcpt_domain = addr->domain;
 
 #ifdef SUPPORT_I18N
@@ -703,180 +762,201 @@ tls_retry_connection:
        }
 #endif
 
-      new_domain_record.result =
-        (old_domain_cache_result == ccache_reject_mfnull)?
-          ccache_reject_mfnull: ccache_accept;
-
-      /* Do the random local part check first */
-
-      if (random_local_part != NULL)
-        {
-        uschar randombuffer[1024];
-        BOOL random_ok =
-          smtp_write_command(&sx.outblock, FALSE,
-            "RCPT TO:<%.1000s@%.1000s>\r\n", random_local_part,
-            rcpt_domain) >= 0 &&
-          smtp_read_response(&sx.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.
-       However, some servers drop the connection after responding to  an
-       invalid recipient, so on (any) error we drop and remake the connection.
-       */
-
-        else if (errno == 0)
-          {
-         /* This would be ok for 1st rcpt a cutthrough, but no way to
-         handle a subsequent.  So refuse to support any */
-         cancel_cutthrough_connection("random-recipient");
+      /* This would be ok for 1st rcpt of a cutthrough (the case handled here;
+      subsequents are done in cutthrough_multi()), but no way to
+      handle a subsequent because of the RSET vaporising the MAIL FROM.
+      So refuse to support any.  Most cutthrough use will not involve
+      random_local_part, so no loss. */
+      cancel_cutthrough_connection(TRUE, US"random-recipient");
+
+      addr->address = string_sprintf("%s@%.1000s",
+                                   random_local_part, rcpt_domain);
+      done = FALSE;
+
+      /* If accepted, we aren't going to do any further tests below.
+      Otherwise, cache a real negative response, and get back to the right
+      state to send RCPT. Unless there's some problem such as a dropped
+      connection, we expect to succeed, because the commands succeeded above.
+      However, some servers drop the connection after responding to an
+      invalid recipient, so on (any) error we drop and remake the connection.
+      XXX We don't care about that for postmaster_full.  Should we?
+
+      XXX could we add another flag to the context, and have the common
+      code emit the RSET too?  Even pipelined after the RCPT...
+      Then the main-verify call could use it if there's to be a subsequent
+      postmaster-verify.
+      The sync_responses() would need to be taught about it and we'd
+      need another return code filtering out to here.
+
+      Avoid using a SIZE option on the MAIL for all random-rcpt checks.
+      */
 
-          if (randombuffer[0] == '5')
-            new_domain_record.random_result = ccache_reject;
+      sx.avoid_option = OPTION_SIZE;
 
-          done =
-            smtp_write_command(&sx.outblock, FALSE, "RSET\r\n") >= 0 &&
-            smtp_read_response(&sx.inblock, responsebuffer, sizeof(responsebuffer),
-              '2', callout) &&
+      /* Remember when we last did a random test */
+      new_domain_record.random_stamp = time(NULL);
 
-            smtp_write_command(&sx.outblock, FALSE,
-#ifdef SUPPORT_I18N
-             addr->prop.utf8_msg && !addr->prop.utf8_downcvt
-             ? "MAIL FROM:<%s> SMTPUTF8\r\n"
-             :
-#endif
-               "MAIL FROM:<%s>\r\n",
-              from_address) >= 0 &&
-            smtp_read_response(&sx.inblock, responsebuffer, sizeof(responsebuffer),
-              '2', callout);
+      if (smtp_write_mail_and_rcpt_cmds(&sx, &yield) == 0)
+       switch(addr->transport_return)
+         {
+         case PENDING_OK:      /* random was accepted, unfortunately */
+           new_domain_record.random_result = ccache_accept;
+           yield = OK;         /* Only usable verify result we can return */
+           done = TRUE;
+           *failure_ptr = US"random";
+           goto no_conn;
+         case FAIL:            /* rejected: the preferred result */
+           new_domain_record.random_result = ccache_reject;
+           sx.avoid_option = 0;
+
+           /* Between each check, issue RSET, because some servers accept only
+           one recipient after MAIL FROM:<>.
+           XXX We don't care about that for postmaster_full.  Should we? */
+
+           if ((done =
+             smtp_write_command(&sx.outblock, SCMD_FLUSH, "RSET\r\n") >= 0 &&
+             smtp_read_response(&sx.inblock, sx.buffer, sizeof(sx.buffer),
+               '2', callout)))
+             break;
 
-         if (!done)
-           {
            HDEBUG(D_acl|D_v)
-             debug_printf("problem after random/rset/mfrom; reopen conn\n");
+             debug_printf_indent("problem after random/rset/mfrom; reopen conn\n");
            random_local_part = NULL;
 #ifdef SUPPORT_TLS
-           tls_close(FALSE, TRUE);
+           tls_close(sx.cctx.tls_ctx, TLS_SHUTDOWN_NOWAIT);
 #endif
-           HDEBUG(D_transport|D_acl|D_v) debug_printf("  SMTP(close)>>\n");
-           (void)close(sx.inblock.sock);
+           HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP(close)>>\n");
+           (void)close(sx.cctx.sock);
+           sx.cctx.sock = -1;
 #ifndef DISABLE_EVENT
            (void) event_raise(addr->transport->event_action,
                              US"tcp:close", NULL);
 #endif
+           addr->address = main_address;
+           addr->transport_return = PENDING_DEFER;
+           sx.first_addr = sx.sync_addr = addr;
+           sx.ok = FALSE;
+           sx.send_rset = TRUE;
+           sx.completed_addr = FALSE;
            goto tls_retry_connection;
-           }
-          }
-        else done = FALSE;    /* Some timeout/connection problem */
-        }                     /* Random check */
+         case DEFER:           /* 4xx response to random */
+           break;              /* Just to be clear. ccache_unknown, !done. */
+         }
 
-      /* 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. */
+      /* Re-setup for main verify, or for the error message when failing */
+      addr->address = main_address;
+      addr->transport_return = PENDING_DEFER;
+      sx.first_addr = sx.sync_addr = addr;
+      sx.ok = FALSE;
+      sx.send_rset = TRUE;
+      sx.completed_addr = FALSE;
+      }
+    else
+      done = TRUE;
 
-      if (new_domain_record.random_result != ccache_accept && done)
-        {
-        /* Get the rcpt_include_affixes flag from the transport if there is one,
-        but assume FALSE if there is not. */
+    /* Main verify.  For rcpt-verify use SIZE if we know it and we're not cacheing;
+    for sndr-verify never use it. */
 
-       uschar * rcpt = transport_rcpt_address(addr,
-              addr->transport ? addr->transport->rcpt_include_affixes : FALSE);
+    if (done)
+      {
+      if (!(options & vopt_is_recipient  &&  options & vopt_callout_no_cache))
+       sx.avoid_option = OPTION_SIZE;
 
-#ifdef SUPPORT_I18N
-       /*XXX should the conversion be moved into transport_rcpt_address() ? */
-       if (  testflag(addr, af_utf8_downcvt)
-          && !(rcpt = string_address_utf8_to_alabel(rcpt, NULL))
-          )
-         {
-         errno = ERRNO_EXPANDFAIL;
-         *failure_ptr = US"recipient";
-         done = FALSE;
-         }
-       else
-#endif
+      done = FALSE;
+      switch(smtp_write_mail_and_rcpt_cmds(&sx, &yield))
+       {
+       case 0:  switch(addr->transport_return) /* ok so far */
+                   {
+                   case PENDING_OK:  done = TRUE;
+                                     new_address_record.result = ccache_accept;
+                                     break;
+                   case FAIL:      done = TRUE;
+                                     yield = FAIL;
+                                     *failure_ptr = US"recipient";
+                                     new_address_record.result = ccache_reject;
+                                     break;
+                   default:        break;
+                   }
+                 break;
+
+       case -1:                                /* MAIL response error */
+                 *failure_ptr = US"mail";
+                 if (errno == 0 && sx.buffer[0] == '5')
+                   {
+                   setflag(addr, af_verify_nsfail);
+                   if (from_address[0] == 0)
+                     new_domain_record.result = ccache_reject_mfnull;
+                   }
+                 break;
+                                               /* non-MAIL read i/o error */
+                                               /* non-MAIL response timeout */
+                                               /* internal error; channel still usable */
+       default:  break;                        /* transmit failed */
+       }
+      }
 
-        done =
-          smtp_write_command(&sx.outblock, FALSE, "RCPT TO:<%.1000s>\r\n",
-            rcpt) >= 0 &&
-          smtp_read_response(&sx.inblock, responsebuffer, sizeof(responsebuffer),
-            '2', callout);
+    addr->auth_sndr = client_authenticated_sender;
 
-        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;
-          }
+    deliver_host = deliver_host_address = NULL;
+    deliver_domain = save_deliver_domain;
 
-        /* Do postmaster check if requested; if a full check is required, we
-        check for RCPT TO:<postmaster> (no domain) in accordance with RFC 821. */
+    /* Do postmaster check if requested; if a full check is required, we
+    check for RCPT TO:<postmaster> (no domain) in accordance with RFC 821. */
 
-        if (done && pm_mailfrom)
-          {
-          /* Could possibly shift before main verify, just above, and be ok
-         for cutthrough.  But no way to handle a subsequent rcpt, so just
-         refuse any */
-       cancel_cutthrough_connection("postmaster verify");
-       HDEBUG(D_acl|D_v) debug_printf("Cutthrough cancelled by presence of postmaster verify\n");
-
-          done =
-            smtp_write_command(&sx.outblock, FALSE, "RSET\r\n") >= 0 &&
-            smtp_read_response(&sx.inblock, responsebuffer,
-              sizeof(responsebuffer), '2', callout) &&
-
-            smtp_write_command(&sx.outblock, FALSE,
-              "MAIL FROM:<%s>\r\n", pm_mailfrom) >= 0 &&
-            smtp_read_response(&sx.inblock, responsebuffer,
-              sizeof(responsebuffer), '2', callout) &&
-
-            /* First try using the current domain */
-
-            ((
-            smtp_write_command(&sx.outblock, FALSE,
-              "RCPT TO:<postmaster@%.1000s>\r\n", rcpt_domain) >= 0 &&
-            smtp_read_response(&sx.inblock, responsebuffer,
-              sizeof(responsebuffer), '2', callout)
-            )
-
-            ||
-
-            /* If that doesn't work, and a full check is requested,
-            try without the domain. */
-
-            (
-            (options & vopt_callout_fullpm) != 0 &&
-            smtp_write_command(&sx.outblock, FALSE,
-              "RCPT TO:<postmaster>\r\n") >= 0 &&
-            smtp_read_response(&sx.inblock, responsebuffer,
-              sizeof(responsebuffer), '2', callout)
-            ));
-
-          /* Sort out the cache record */
-
-          new_domain_record.postmaster_stamp = time(NULL);
-
-          if (done)
-            new_domain_record.postmaster_result = ccache_accept;
-          else if (errno == 0 && 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 */
+    if (done && pm_mailfrom)
+      {
+      /* Could possibly shift before main verify, just above, and be ok
+      for cutthrough.  But no way to handle a subsequent rcpt, so just
+      refuse any */
+      cancel_cutthrough_connection(TRUE, US"postmaster verify");
+      HDEBUG(D_acl|D_v) debug_printf_indent("Cutthrough cancelled by presence of postmaster verify\n");
 
+      done = smtp_write_command(&sx.outblock, SCMD_FLUSH, "RSET\r\n") >= 0
+          && smtp_read_response(&sx.inblock, sx.buffer,
+                               sizeof(sx.buffer), '2', callout);
+
+      if (done)
+       {
+       uschar * main_address = addr->address;
+
+       /*XXX oops, affixes */
+       addr->address = string_sprintf("postmaster@%.1000s", addr->domain);
+       addr->transport_return = PENDING_DEFER;
+
+       sx.from_addr = pm_mailfrom;
+       sx.first_addr = sx.sync_addr = addr;
+       sx.ok = FALSE;
+       sx.send_rset = TRUE;
+       sx.completed_addr = FALSE;
+       sx.avoid_option = OPTION_SIZE;
+
+       if(  smtp_write_mail_and_rcpt_cmds(&sx, &yield) == 0
+         && addr->transport_return == PENDING_OK
+         )
+         done = TRUE;
+       else
+         done = (options & vopt_callout_fullpm) != 0
+             && smtp_write_command(&sx.outblock, SCMD_FLUSH,
+                           "RCPT TO:<postmaster>\r\n") >= 0
+             && smtp_read_response(&sx.inblock, sx.buffer,
+                           sizeof(sx.buffer), '2', callout);
+
+       /* Sort out the cache record */
+
+       new_domain_record.postmaster_stamp = time(NULL);
+
+       if (done)
+         new_domain_record.postmaster_result = ccache_accept;
+       else if (errno == 0 && sx.buffer[0] == '5')
+         {
+         *failure_ptr = US"postmaster";
+         setflag(addr, af_verify_pmfail);
+         new_domain_record.postmaster_result = ccache_reject;
+         }
+
+       addr->address = main_address;
+       }
+      }
     /* For any failure of the main check, other than a negative response, we just
     close the connection and carry on. We can identify a negative response by the
     fact that errno is zero. For I/O errors it will be non-zero
@@ -888,7 +968,7 @@ tls_retry_connection:
     is not to be widely broadcast. */
 
 no_conn:
-    if (!done) switch(errno)
+    switch(errno)
       {
       case ETIMEDOUT:
        HDEBUG(D_verify) debug_printf("SMTP timeout\n");
@@ -901,8 +981,7 @@ no_conn:
        extern int acl_where;   /* src/acl.c */
        errno = 0;
        addr->message = string_sprintf(
-           "response to \"EHLO\" from %s [%s] did not include SMTPUTF8",
-           host->name, host->address);
+           "response to \"EHLO\" did not include SMTPUTF8");
        addr->user_message = acl_where == ACL_WHERE_RCPT
          ? US"533 no support for internationalised mailbox name"
          : US"550 mailbox unavailable";
@@ -910,27 +989,38 @@ no_conn:
        done = TRUE;
        }
        break;
+#endif
+#if defined(SUPPORT_TLS) && defined(EXPERIMENTAL_REQUIRETLS)
+      case ERRNO_REQUIRETLS:
+        addr->user_message = US"530 5.7.4 REQUIRETLS support required";
+       yield = FAIL;
+       done = TRUE;
+       break;
 #endif
       case ECONNREFUSED:
        sx.send_quit = FALSE;
        break;
 
       case 0:
-       if (*responsebuffer == 0) Ustrcpy(responsebuffer, US"connection dropped");
+       if (*sx.buffer == 0) Ustrcpy(sx.buffer, US"connection dropped");
 
-       addr->message =
-         string_sprintf("response to \"%s\" from %s [%s] was: %s",
-           big_buffer, host->name, host->address,
-           string_printing(responsebuffer));
+       /*XXX test here is ugly; seem to have a split of responsibility for
+       building this message.  Need to rationalise.  Where is it done
+       before here, and when not?
+       Not == 5xx resp to MAIL on main-verify
+       */
+       if (!addr->message) addr->message =
+         string_sprintf("response to \"%s\" was: %s",
+                         big_buffer, string_printing(sx.buffer));
 
        addr->user_message = options & vopt_is_recipient
-         ? string_sprintf("Callout verification failed:\n%s", responsebuffer)
+         ? string_sprintf("Callout verification failed:\n%s", sx.buffer)
          : string_sprintf("Called:   %s\nSent:     %s\nResponse: %s",
-           host->address, big_buffer, responsebuffer);
+           host->address, big_buffer, sx.buffer);
 
        /* Hard rejection ends the process */
 
-       if (responsebuffer[0] == '5')   /* Address rejected */
+       if (sx.buffer[0] == '5')   /* Address rejected */
          {
          yield = FAIL;
          done = TRUE;
@@ -942,8 +1032,33 @@ no_conn:
 
     /* Cutthrough - on a successful connect and recipient-verify with
     use-sender and we are 1st rcpt and have no cutthrough conn so far
-    here is where we want to leave the conn open */
-    if (  cutthrough.delivery
+    here is where we want to leave the conn open.  Ditto for a lazy-close
+    verify. */
+
+    if (cutthrough.delivery)
+      {
+      if (addr->transport->filter_command)
+        {
+        cutthrough.delivery= FALSE;
+        HDEBUG(D_acl|D_v) debug_printf("Cutthrough cancelled by presence of transport filter\n");
+        }
+#ifndef DISABLE_DKIM
+      if (ob->dkim.dkim_domain)
+        {
+        cutthrough.delivery= FALSE;
+        HDEBUG(D_acl|D_v) debug_printf("Cutthrough cancelled by presence of DKIM signing\n");
+        }
+#endif
+#ifdef EXPERIMENTAL_ARC
+      if (ob->arc_sign)
+        {
+        cutthrough.delivery= FALSE;
+        HDEBUG(D_acl|D_v) debug_printf("Cutthrough cancelled by presence of ARC signing\n");
+        }
+#endif
+      }
+
+    if (  (cutthrough.delivery || options & vopt_callout_hold)
        && rcpt_count == 1
        && done
        && yield == OK
@@ -951,120 +1066,102 @@ no_conn:
           == vopt_callout_recipsender
        && !random_local_part
        && !pm_mailfrom
-       && cutthrough.fd < 0
+       && cutthrough.cctx.sock < 0
        && !sx.lmtp
        )
       {
-      HDEBUG(D_acl|D_v) debug_printf("holding verify callout open for cutthrough delivery\n");
-
-      cutthrough.fd = sx.outblock.sock;        /* We assume no buffer in use in the outblock */
-      cutthrough.nrcpt = 1;
-      cutthrough.interface = interface;
-      cutthrough.host = *host;
-      cutthrough.addr = *addr;         /* Save the address_item for later logging */
-      cutthrough.addr.next =     NULL;
+      address_item * parent, * caddr;
+
+      HDEBUG(D_acl|D_v) debug_printf_indent("holding verify callout open for %s\n",
+       cutthrough.delivery
+       ? "cutthrough delivery" : "potential further verifies and delivery");
+
+      cutthrough.callout_hold_only = !cutthrough.delivery;
+      cutthrough.is_tls =      tls_out.active.sock >= 0;
+      /* We assume no buffer in use in the outblock */
+      cutthrough.cctx =                sx.cctx;
+      cutthrough.nrcpt =       1;
+      cutthrough.transport =   addr->transport->name;
+      cutthrough.interface =   interface;
+      cutthrough.snd_port =    sending_port;
+      cutthrough.peer_options =        smtp_peer_options;
+      cutthrough.host =                *host;
+       {
+       int oldpool = store_pool;
+       store_pool = POOL_PERM;
+       cutthrough.snd_ip = string_copy(sending_ip_address);
+       cutthrough.host.name = string_copy(host->name);
+       cutthrough.host.address = string_copy(host->address);
+       store_pool = oldpool;
+       }
+
+      /* Save the address_item and parent chain for later logging */
+      cutthrough.addr =                *addr;
+      cutthrough.addr.next =   NULL;
       cutthrough.addr.host_used = &cutthrough.host;
-      if (addr->parent)
-        *(cutthrough.addr.parent = store_get(sizeof(address_item))) =
-         *addr->parent;
+      for (caddr = &cutthrough.addr, parent = addr->parent;
+          parent;
+          parent = parent->parent)
+        *(caddr->parent = store_get(sizeof(address_item))) = *parent;
+
       ctblock.buffer = ctbuffer;
       ctblock.buffersize = sizeof(ctbuffer);
       ctblock.ptr = ctbuffer;
       /* ctblock.cmd_count = 0; ctblock.authenticating = FALSE; */
-      ctblock.sock = cutthrough.fd;
+      ctblock.cctx = &cutthrough.cctx;
       }
     else
       {
-      /* Ensure no cutthrough on multiple address verifies */
+      /* Ensure no cutthrough on multiple verifies that were incompatible */
       if (options & vopt_callout_recipsender)
-        cancel_cutthrough_connection("not usable for cutthrough");
+        cancel_cutthrough_connection(TRUE, US"not usable for cutthrough");
       if (sx.send_quit)
        {
-       (void) smtp_write_command(&sx.outblock, FALSE, "QUIT\r\n");
+       (void) smtp_write_command(&sx.outblock, SCMD_FLUSH, "QUIT\r\n");
 
        /* Wait a short time for response, and discard it */
-       smtp_read_response(&sx.inblock, responsebuffer, sizeof(responsebuffer),
+       smtp_read_response(&sx.inblock, sx.buffer, sizeof(sx.buffer),
          '2', 1);
        }
 
-      if (sx.inblock.sock >= 0)
+      if (sx.cctx.sock >= 0)
        {
 #ifdef SUPPORT_TLS
-       tls_close(FALSE, TRUE);
+       if (sx.cctx.tls_ctx)
+         {
+         tls_close(sx.cctx.tls_ctx, TLS_SHUTDOWN_NOWAIT);
+         sx.cctx.tls_ctx = NULL;
+         }
 #endif
-       HDEBUG(D_transport|D_acl|D_v) debug_printf("  SMTP(close)>>\n");
-       (void)close(sx.inblock.sock);
-       sx.inblock.sock = sx.outblock.sock = -1;
+       HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP(close)>>\n");
+       (void)close(sx.cctx.sock);
+       sx.cctx.sock = -1;
 #ifndef DISABLE_EVENT
        (void) event_raise(addr->transport->event_action, US"tcp:close", NULL);
 #endif
        }
       }
 
+    if (!done || yield != OK)
+      addr->message = string_sprintf("%s [%s] : %s", host->name, host->address,
+                                   addr->message);
     }    /* Loop through all hosts, while !done */
   }
 
 /* If we get here with done == TRUE, a successful callout happened, and yield
 will be set OK or FAIL according to the response to the RCPT command.
 Otherwise, we looped through the hosts but couldn't complete the business.
-However, there may be domain-specific information to cache in both cases.
-
-The value of the result field in the new_domain record is ccache_unknown if
-there was an error before or with MAIL FROM:, and errno was not zero,
-implying some kind of I/O error. We don't want to write the cache in that case.
-Otherwise the value is ccache_accept, ccache_reject, or ccache_reject_mfnull. */
+However, there may be domain-specific information to cache in both cases. */
 
-if (  !(options & vopt_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 for %s:\n"
-      "  result=%d postmaster=%d random=%d\n",
-      addr->domain,
-      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 (  !(options & vopt_callout_no_cache)
-     && new_address_record.result != ccache_unknown)
-    {
-    if (!dbm_file)
-      dbm_file = dbfn_open(US"callout", O_RDWR|O_CREAT, &dbblock, FALSE);
-    if (!dbm_file)
-      {
-      HDEBUG(D_verify) debug_printf("no callout cache available\n");
-      }
-    else
-      {
-      (void)dbfn_write(dbm_file, address_key, &new_address_record,
-        (int)sizeof(dbdata_callout_cache_address));
-      HDEBUG(D_verify) debug_printf("wrote %s callout cache address record for %s\n",
-        new_address_record.result == ccache_accept ? "positive" : "negative",
-       address_key);
-      }
-    }
-  }    /* done */
+if (!(options & vopt_callout_no_cache))
+  cache_callout_write(&new_domain_record, addr->domain,
+    done, &new_address_record, address_key);
 
 /* Failure to connect to any host, or any response other than 2xx or 5xx is a
 temporary error. If there was only one host, and a response was received, leave
 it alone if supplying details. Otherwise, give a generic response. */
 
-else   /* !done */
+if (!done)
   {
   uschar * dullmsg = string_sprintf("Could not complete %s verify callout",
     options & vopt_is_recipient ? "recipient" : "sender");
@@ -1093,7 +1190,6 @@ else   /* !done */
 /* Come here from within the cache-reading code on fast-track exit. */
 
 END_CALLOUT:
-if (dbm_file) dbfn_close(dbm_file);
 tls_modify_variables(&tls_in);
 return yield;
 }
@@ -1104,7 +1200,7 @@ return yield;
    one was requested and a recipient-verify wasn't subsequently done.
 */
 int
-open_cutthrough_connection( address_item * addr )
+open_cutthrough_connection(address_item * addr)
 {
 address_item addr2;
 int rc;
@@ -1114,7 +1210,7 @@ int rc;
 get rewritten. */
 
 addr2 = *addr;
-HDEBUG(D_acl) debug_printf("----------- %s cutthrough setup ------------\n",
+HDEBUG(D_acl) debug_printf_indent("----------- %s cutthrough setup ------------\n",
   rcpt_count > 1 ? "more" : "start");
 rc = verify_address(&addr2, NULL,
        vopt_is_recipient | vopt_callout_recipsender | vopt_callout_no_cache,
@@ -1122,7 +1218,7 @@ rc = verify_address(&addr2, NULL,
        NULL, NULL, NULL);
 addr->message = addr2.message;
 addr->user_message = addr2.user_message;
-HDEBUG(D_acl) debug_printf("----------- end cutthrough setup ------------\n");
+HDEBUG(D_acl) debug_printf_indent("----------- end cutthrough setup ------------\n");
 return rc;
 }
 
@@ -1132,14 +1228,16 @@ return rc;
 static BOOL
 cutthrough_send(int n)
 {
-if(cutthrough.fd < 0)
+if(cutthrough.cctx.sock < 0)
   return TRUE;
 
 if(
 #ifdef SUPPORT_TLS
-   (tls_out.active == cutthrough.fd) ? tls_write(FALSE, ctblock.buffer, n) :
+   cutthrough.is_tls
+   ? tls_write(cutthrough.cctx.tls_ctx, ctblock.buffer, n, FALSE)
+   :
 #endif
-   send(cutthrough.fd, ctblock.buffer, n, 0) > 0
+     send(cutthrough.cctx.sock, ctblock.buffer, n, 0) > 0
   )
 {
   transport_count += n;
@@ -1147,7 +1245,7 @@ if(
   return TRUE;
 }
 
-HDEBUG(D_transport|D_acl) debug_printf("cutthrough_send failed: %s\n", strerror(errno));
+HDEBUG(D_transport|D_acl) debug_printf_indent("cutthrough_send failed: %s\n", strerror(errno));
 return FALSE;
 }
 
@@ -1168,20 +1266,27 @@ return TRUE;
 }
 
 /* Buffered output of counted data block.   Return boolean success */
-BOOL
+static BOOL
 cutthrough_puts(uschar * cp, int n)
 {
-if (cutthrough.fd < 0)       return TRUE;
-if (_cutthrough_puts(cp, n)) return TRUE;
-cancel_cutthrough_connection("transmit failed");
+if (cutthrough.cctx.sock < 0) return TRUE;
+if (_cutthrough_puts(cp, n))  return TRUE;
+cancel_cutthrough_connection(TRUE, US"transmit failed");
 return FALSE;
 }
 
+void
+cutthrough_data_puts(uschar * cp, int n)
+{
+if (cutthrough.delivery) (void) cutthrough_puts(cp, n);
+return;
+}
+
 
 static BOOL
 _cutthrough_flush_send(void)
 {
-int n= ctblock.ptr-ctblock.buffer;
+int n = ctblock.ptr - ctblock.buffer;
 
 if(n>0)
   if(!cutthrough_send(n))
@@ -1195,21 +1300,28 @@ BOOL
 cutthrough_flush_send(void)
 {
 if (_cutthrough_flush_send()) return TRUE;
-cancel_cutthrough_connection("transmit failed");
+cancel_cutthrough_connection(TRUE, US"transmit failed");
 return FALSE;
 }
 
 
-BOOL
+static BOOL
 cutthrough_put_nl(void)
 {
 return cutthrough_puts(US"\r\n", 2);
 }
 
 
+void
+cutthrough_data_put_nl(void)
+{
+cutthrough_data_puts(US"\r\n", 2);
+}
+
+
 /* Get and check response from cutthrough target */
 static uschar
-cutthrough_response(char expect, uschar ** copy, int timeout)
+cutthrough_response(client_conn_ctx * cctx, char expect, uschar ** copy, int timeout)
 {
 smtp_inblock inblock;
 uschar inbuffer[4096];
@@ -1219,12 +1331,11 @@ inblock.buffer = inbuffer;
 inblock.buffersize = sizeof(inbuffer);
 inblock.ptr = inbuffer;
 inblock.ptrend = inbuffer;
-inblock.sock = cutthrough.fd;
-/* this relies on (inblock.sock == tls_out.active) */
+inblock.cctx = cctx;
 if(!smtp_read_response(&inblock, responsebuffer, sizeof(responsebuffer), expect, timeout))
-  cancel_cutthrough_connection("target timeout on read");
+  cancel_cutthrough_connection(TRUE, US"target timeout on read");
 
-if(copy != NULL)
+if(copy)
   {
   uschar * cp;
   *copy = cp = string_copy(responsebuffer);
@@ -1242,21 +1353,21 @@ return responsebuffer[0];
 BOOL
 cutthrough_predata(void)
 {
-if(cutthrough.fd < 0)
+if(cutthrough.cctx.sock < 0 || cutthrough.callout_hold_only)
   return FALSE;
 
-HDEBUG(D_transport|D_acl|D_v) debug_printf("  SMTP>> DATA\n");
+HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP>> DATA\n");
 cutthrough_puts(US"DATA\r\n", 6);
 cutthrough_flush_send();
 
 /* Assume nothing buffered.  If it was it gets ignored. */
-return cutthrough_response('3', NULL, CUTTHROUGH_DATA_TIMEOUT) == '3';
+return cutthrough_response(&cutthrough.cctx, '3', NULL, CUTTHROUGH_DATA_TIMEOUT) == '3';
 }
 
 
-/* fd and tctx args only to match write_chunk() */
+/* tctx arg only to match write_chunk() */
 static BOOL
-cutthrough_write_chunk(int fd, transport_ctx * tctx, uschar * s, int len)
+cutthrough_write_chunk(transport_ctx * tctx, uschar * s, int len)
 {
 uschar * s2;
 while(s && (s2 = Ustrchr(s, '\n')))
@@ -1277,61 +1388,83 @@ cutthrough_headers_send(void)
 {
 transport_ctx tctx;
 
-if(cutthrough.fd < 0)
+if(cutthrough.cctx.sock < 0 || cutthrough.callout_hold_only)
   return FALSE;
 
 /* We share a routine with the mainline transport to handle header add/remove/rewrites,
    but having a separate buffered-output function (for now)
 */
-HDEBUG(D_acl) debug_printf("----------- start cutthrough headers send -----------\n");
+HDEBUG(D_acl) debug_printf_indent("----------- start cutthrough headers send -----------\n");
 
+tctx.u.fd = cutthrough.cctx.sock;
 tctx.tblock = cutthrough.addr.transport;
 tctx.addr = &cutthrough.addr;
 tctx.check_string = US".";
 tctx.escape_string = US"..";
+/*XXX check under spool_files_wireformat.  Might be irrelevant */
 tctx.options = topt_use_crlf;
 
-if (!transport_headers_send(cutthrough.fd, &tctx, &cutthrough_write_chunk))
+if (!transport_headers_send(&tctx, &cutthrough_write_chunk))
   return FALSE;
 
-HDEBUG(D_acl) debug_printf("----------- done cutthrough headers send ------------\n");
+HDEBUG(D_acl) debug_printf_indent("----------- done cutthrough headers send ------------\n");
 return TRUE;
 }
 
 
 static void
-close_cutthrough_connection(const char * why)
+close_cutthrough_connection(const uschar * why)
 {
-if(cutthrough.fd >= 0)
+int fd = cutthrough.cctx.sock;
+if(fd >= 0)
   {
   /* We could be sending this after a bunch of data, but that is ok as
      the only way to cancel the transfer in dataphase is to drop the tcp
      conn before the final dot.
   */
+  client_conn_ctx tmp_ctx = cutthrough.cctx;
   ctblock.ptr = ctbuffer;
-  HDEBUG(D_transport|D_acl|D_v) debug_printf("  SMTP>> QUIT\n");
+  HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP>> QUIT\n");
   _cutthrough_puts(US"QUIT\r\n", 6);   /* avoid recursion */
   _cutthrough_flush_send();
+  cutthrough.cctx.sock = -1;           /* avoid recursion via read timeout */
+  cutthrough.nrcpt = 0;                        /* permit re-cutthrough on subsequent message */
 
   /* Wait a short time for response, and discard it */
-  cutthrough_response('2', NULL, 1);
-
-  #ifdef SUPPORT_TLS
-  tls_close(FALSE, TRUE);
-  #endif
-  HDEBUG(D_transport|D_acl|D_v) debug_printf("  SMTP(close)>>\n");
-  (void)close(cutthrough.fd);
-  cutthrough.fd = -1;
-  HDEBUG(D_acl) debug_printf("----------- cutthrough shutdown (%s) ------------\n", why);
+  cutthrough_response(&tmp_ctx, '2', NULL, 1);
+
+#ifdef SUPPORT_TLS
+  if (cutthrough.is_tls)
+    {
+    tls_close(cutthrough.cctx.tls_ctx, TLS_SHUTDOWN_NOWAIT);
+    cutthrough.cctx.tls_ctx = NULL;
+    cutthrough.is_tls = FALSE;
+    }
+#endif
+  HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP(close)>>\n");
+  (void)close(fd);
+  HDEBUG(D_acl) debug_printf_indent("----------- cutthrough shutdown (%s) ------------\n", why);
   }
 ctblock.ptr = ctbuffer;
 }
 
 void
-cancel_cutthrough_connection(const char * why)
+cancel_cutthrough_connection(BOOL close_noncutthrough_verifies, const uschar * why)
 {
-close_cutthrough_connection(why);
-cutthrough.delivery = FALSE;
+if (cutthrough.delivery || close_noncutthrough_verifies)
+  close_cutthrough_connection(why);
+cutthrough.delivery = cutthrough.callout_hold_only = FALSE;
+}
+
+
+void
+release_cutthrough_connection(const uschar * why)
+{
+if (cutthrough.cctx.sock < 0) return;
+HDEBUG(D_acl) debug_printf_indent("release cutthrough conn: %s\n", why);
+cutthrough.cctx.sock = -1;
+cutthrough.cctx.tls_ctx = NULL;
+cutthrough.delivery = cutthrough.callout_hold_only = FALSE;
 }
 
 
@@ -1347,7 +1480,7 @@ cutthrough_finaldot(void)
 {
 uschar res;
 address_item * addr;
-HDEBUG(D_transport|D_acl|D_v) debug_printf("  SMTP>> .\n");
+HDEBUG(D_transport|D_acl|D_v) debug_printf_indent("  SMTP>> .\n");
 
 /* Assume data finshed with new-line */
 if(  !cutthrough_puts(US".", 1)
@@ -1356,7 +1489,8 @@ if(  !cutthrough_puts(US".", 1)
   )
   return cutthrough.addr.message;
 
-res = cutthrough_response('2', &cutthrough.addr.message, CUTTHROUGH_DATA_TIMEOUT);
+res = cutthrough_response(&cutthrough.cctx, '2', &cutthrough.addr.message,
+       CUTTHROUGH_DATA_TIMEOUT);
 for (addr = &cutthrough.addr; addr; addr = addr->next)
   {
   addr->message = cutthrough.addr.message;
@@ -1364,7 +1498,7 @@ for (addr = &cutthrough.addr; addr; addr = addr->next)
     {
     case '2':
       delivery_log(LOG_MAIN, addr, (int)'>', NULL);
-      close_cutthrough_connection("delivered");
+      close_cutthrough_connection(US"delivered");
       break;
 
     case '4':
@@ -1449,7 +1583,7 @@ va_list ap;
 
 va_start(ap, format);
 if (smtp_out && (f == smtp_out))
-  smtp_vprintf(format, ap);
+  smtp_vprintf(format, FALSE, ap);
 else
   vfprintf(f, format, ap);
 va_end(ap);
@@ -1552,9 +1686,9 @@ else ko_prefix = cr = US"";
 
 if (parse_find_at(address) == NULL)
   {
-  if ((options & vopt_qualify) == 0)
+  if (!(options & vopt_qualify))
     {
-    if (f != NULL)
+    if (f)
       respond_printf(f, "%sA domain is required for \"%s\"%s\n",
         ko_prefix, address, cr);
     *failure_ptr = US"qualify";
@@ -1572,7 +1706,7 @@ DEBUG(D_verify)
 /* 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)
+if (global_rewrite_rules)
   {
   uschar *old = address;
   address = rewrite_address(address, options & vopt_is_recipient, FALSE,
@@ -1581,21 +1715,21 @@ if (global_rewrite_rules != NULL)
     {
     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 (f && !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)
+if (!(options & (vopt_fake_sender|vopt_is_recipient)))
   sender_address = address;
 
 /* If the address was rewritten to <> no verification can be done, and we have
 to return OK. This rewriting is permitted only for sender addresses; for other
 addresses, such rewriting fails. */
 
-if (address[0] == 0) return OK;
+if (!address[0]) return OK;
 
 /* Flip the legacy TLS-related variables over to the outbound set in case
 they're used in the context of a transport used by verification. Reset them
@@ -1647,7 +1781,7 @@ while (addr_new)
   if (testflag(addr, af_pfr))
     {
     allok = FALSE;
-    if (f != NULL)
+    if (f)
       {
       BOOL allow;
 
@@ -1658,8 +1792,8 @@ while (addr_new)
         }
       else
         {
-        allow = (addr->address[0] == '|')?
-          testflag(addr, af_allow_pipe) : testflag(addr, af_allow_file);
+        allow = addr->address[0] == '|'
+          testflag(addr, af_allow_pipe) : testflag(addr, af_allow_file);
         fprintf(f, "%s -> %s", addr->parent->address, addr->address);
         }
 
@@ -1711,16 +1845,16 @@ while (addr_new)
       transport. */
 
       transport_feedback tf = {
-        NULL,                       /* interface (=> any) */
-        US"smtp",                   /* port */
-        US"smtp",                   /* protocol */
-        NULL,                       /* hosts */
-        US"$smtp_active_hostname",  /* helo_data */
-        FALSE,                      /* hosts_override */
-        FALSE,                      /* hosts_randomize */
-        FALSE,                      /* gethostbyname */
-        TRUE,                       /* qualify_single */
-        FALSE                       /* search_parents */
+        .interface =           NULL,                       /* interface (=> any) */
+        .port =                        US"smtp",
+        .protocol =            US"smtp",
+        .hosts =               NULL,
+        .helo_data =           US"$smtp_active_hostname",
+        .hosts_override =      FALSE,
+        .hosts_randomize =     FALSE,
+        .gethostbyname =       FALSE,
+        .qualify_single =      TRUE,
+        .search_parents =      FALSE
         };
 
       /* If verification yielded a remote transport, we want to use that
@@ -1767,7 +1901,7 @@ while (addr_new)
             additional host items being inserted into the chain. Hence we must
             save the next host first. */
 
-            flags = HOST_FIND_BY_A;
+            flags = HOST_FIND_BY_A | HOST_FIND_BY_AAAA;
             if (tf.qualify_single) flags |= HOST_FIND_QUALIFY_SINGLE;
             if (tf.search_parents) flags |= HOST_FIND_SEARCH_PARENTS;
 
@@ -1779,16 +1913,16 @@ while (addr_new)
                 (void)host_find_byname(host, NULL, flags, NULL, TRUE);
               else
                {
-               dnssec_domains * dnssec_domains = NULL;
+               const dnssec_domains * dsp = NULL;
                if (Ustrcmp(tp->driver_name, "smtp") == 0)
                  {
                  smtp_transport_options_block * ob =
                      (smtp_transport_options_block *) tp->options_block;
-                 dnssec_domains = &ob->dnssec;
+                 dsp = &ob->dnssec;
                  }
 
-                (void)host_find_bydns(host, NULL, flags, NULL, NULL, NULL,
-                 dnssec_domains, NULL, NULL);
+                (void) host_find_bydns(host, NULL, flags, NULL, NULL, NULL,
+                 dsp, NULL, NULL);
                }
               }
             }
@@ -1814,12 +1948,15 @@ while (addr_new)
 #endif
           rc = do_callout(addr, host_list, &tf, callout, callout_overall,
             callout_connect, options, se_mailfrom, pm_mailfrom);
+#ifdef SUPPORT_TLS
+         deliver_set_expansions(NULL);
+#endif
           }
         }
       else
         {
         HDEBUG(D_verify) debug_printf("Cannot do callout: neither router nor "
-          "transport provided a host list\n");
+          "transport provided a host list, or transport is not smtp\n");
         }
       }
     }
@@ -1863,7 +2000,7 @@ while (addr_new)
         }
       respond_printf(f, "%s\n", cr);
       }
-    cancel_cutthrough_connection("routing hard fail");
+    cancel_cutthrough_connection(TRUE, US"routing hard fail");
 
     if (!full_info)
       {
@@ -1902,7 +2039,7 @@ while (addr_new)
         }
       respond_printf(f, "%s\n", cr);
       }
-    cancel_cutthrough_connection("routing soft fail");
+    cancel_cutthrough_connection(TRUE, US"routing soft fail");
 
     if (!full_info)
       {
@@ -1975,7 +2112,7 @@ while (addr_new)
       /* If stopped because more than one new address, cannot cutthrough */
 
       if (addr_new && addr_new->next)
-       cancel_cutthrough_connection("multiple addresses from routing");
+       cancel_cutthrough_connection(TRUE, US"multiple addresses from routing");
 
       yield = OK;
       goto out;
@@ -2087,7 +2224,7 @@ return yield;
 *************************************************/
 
 /* This function checks those header lines that contain addresses, and verifies
-that all the addresses therein are syntactially correct.
+that all the addresses therein are 5322-syntactially correct.
 
 Arguments:
   msgptr     where to put an error message
@@ -2103,7 +2240,7 @@ header_line *h;
 uschar *colon, *s;
 int yield = OK;
 
-for (h = header_list; h != NULL && yield == OK; h = h->next)
+for (h = header_list; h && yield == OK; h = h->next)
   {
   if (h->type != htype_from &&
       h->type != htype_reply_to &&
@@ -2122,7 +2259,7 @@ for (h = header_list; h != NULL && yield == OK; h = h->next)
 
   parse_allow_group = TRUE;
 
-  while (*s != 0)
+  while (*s)
     {
     uschar *ss = parse_find_address_end(s, FALSE);
     uschar *recipient, *errmess;
@@ -2139,7 +2276,7 @@ for (h = header_list; h != NULL && yield == OK; h = h->next)
     /* 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 (recipient && !domain)
       {
       if (h->type == htype_from || h->type == htype_sender)
         {
@@ -2155,7 +2292,7 @@ for (h = header_list; h != NULL && yield == OK; h = h->next)
     /* 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)
+    if (!recipient && Ustrcmp(errmess, "empty address") != 0)
       {
       uschar *verb = US"is";
       uschar *t = ss;
@@ -2185,7 +2322,7 @@ for (h = header_list; h != NULL && yield == OK; h = h->next)
       /* deconst cast ok as we're passing a non-const to string_printing() */
       *msgptr = US string_printing(
         string_sprintf("%s: failing address in \"%.*s:\" header %s: %.*s",
-          errmess, tt - h->text, h->text, verb, len, s));
+          errmess, (int)(tt - h->text), h->text, verb, len, s));
 
       yield = FAIL;
       break;          /* Out of address loop */
@@ -2193,7 +2330,7 @@ for (h = header_list; h != NULL && yield == OK; h = h->next)
 
     /* Advance to the next address */
 
-    s = ss + (terminator? 1:0);
+    s = ss + (terminator ? 1 : 0);
     while (isspace(*s)) s++;
     }   /* Next address */
 
@@ -2225,18 +2362,16 @@ verify_check_header_names_ascii(uschar **msgptr)
 header_line *h;
 uschar *colon, *s;
 
-for (h = header_list; h != NULL; h = h->next)
+for (h = header_list; h; h = h->next)
   {
-   colon = Ustrchr(h->text, ':');
-   for(s = h->text; s < colon; s++)
-     {
-        if ((*s < 33) || (*s > 126))
-        {
-                *msgptr = string_sprintf("Invalid character in header \"%.*s\" found",
-                                         colon - h->text, h->text);
-                return FAIL;
-        }
-     }
+  colon = Ustrchr(h->text, ':');
+  for(s = h->text; s < colon; s++)
+    if ((*s < 33) || (*s > 126))
+      {
+      *msgptr = string_sprintf("Invalid character in header \"%.*s\" found",
+                            colon - h->text, h->text);
+      return FAIL;
+      }
   }
 return OK;
 }
@@ -2488,7 +2623,7 @@ for (i = 0; i < 3 && !done; i++)
           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);
+            (int)(endname - h->text), h->text, *log_msgptr, (int)(ss - s), s);
           yield = FAIL;
           done = TRUE;
           break;
@@ -2516,11 +2651,9 @@ for (i = 0; i < 3 && !done; i++)
         {
         *verrno = vaddr->basic_errno;
         if (smtp_return_error_details)
-          {
           *user_msgptr = string_sprintf("Rejected after DATA: "
             "could not verify \"%.*s\" header address\n%s: %s",
-            endname - h->text, h->text, vaddr->address, vaddr->message);
-          }
+            (int)(endname - h->text), h->text, vaddr->address, vaddr->message);
         }
 
       /* Success or defer */
@@ -2578,9 +2711,11 @@ Side effect: any received ident value is put in sender_ident (NULL otherwise)
 void
 verify_get_ident(int port)
 {
-int sock, host_af, qlen;
+client_conn_ctx ident_conn_ctx = {0};
+int host_af, qlen;
 int received_sender_port, received_interface_port, n;
 uschar *p;
+blob early_data;
 uschar buffer[2048];
 
 /* Default is no ident. Check whether we want to do an ident check for this
@@ -2597,17 +2732,24 @@ to the incoming interface address. If the sender host address is an IPv6
 address, the incoming interface address will also be IPv6. */
 
 host_af = Ustrchr(sender_host_address, ':') == NULL ? AF_INET : AF_INET6;
-if ((sock = ip_socket(SOCK_STREAM, host_af)) < 0) return;
+if ((ident_conn_ctx.sock = ip_socket(SOCK_STREAM, host_af)) < 0) return;
 
-if (ip_bind(sock, host_af, interface_address, 0) < 0)
+if (ip_bind(ident_conn_ctx.sock, host_af, interface_address, 0) < 0)
   {
   DEBUG(D_ident) debug_printf("bind socket for ident failed: %s\n",
     strerror(errno));
   goto END_OFF;
   }
 
-if (ip_connect(sock, host_af, sender_host_address, port,
-               rfc1413_query_timeout, TRUE) < 0)
+/* Construct and send the query. */
+
+qlen = snprintf(CS buffer, sizeof(buffer), "%d , %d\r\n",
+  sender_host_port, interface_port);
+early_data.data = buffer;
+early_data.len = qlen;
+
+if (ip_connect(ident_conn_ctx.sock, host_af, sender_host_address, port,
+               rfc1413_query_timeout, &early_data) < 0)
   {
   if (errno == ETIMEDOUT && LOGGING(ident_timeout))
     log_write(0, LOG_MAIN, "ident connection to %s timed out",
@@ -2618,16 +2760,6 @@ if (ip_connect(sock, host_af, sender_host_address, port,
   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. */
 
@@ -2640,7 +2772,7 @@ for (;;)
   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);
+  count = ip_recv(&ident_conn_ctx, p, size, rfc1413_query_timeout);
   if (count <= 0) goto END_OFF;  /* Read error or EOF */
 
   /* Scan what we just read, to see if we have reached the terminating \r\n. Be
@@ -2705,7 +2837,7 @@ sender_ident = US string_printing(string_copyn(p, 127));
 DEBUG(D_ident) debug_printf("sender_ident = %s\n", sender_ident);
 
 END_OFF:
-(void)close(sock);
+(void)close(ident_conn_ctx.sock);
 return;
 }
 
@@ -3000,7 +3132,7 @@ if (isquery)
 /* 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)
+if (!sender_host_name)
   {
   HDEBUG(D_host_lookup)
     debug_printf("sender host name required, to match against %s\n", ss);
@@ -3015,8 +3147,7 @@ if (sender_host_name == NULL)
 
 /* Match on the sender host name, using the general matching function */
 
-switch(match_check_string(sender_host_name, ss, -1, TRUE, TRUE, TRUE,
-       valueptr))
+switch(match_check_string(sender_host_name, ss, -1, TRUE, TRUE, TRUE, valueptr))
   {
   case OK:    return OK;
   case DEFER: return DEFER;
@@ -3025,14 +3156,12 @@ switch(match_check_string(sender_host_name, ss, -1, TRUE, TRUE, TRUE,
 /* If there are aliases, try matching on them. */
 
 aliases = sender_host_aliases;
-while (*aliases != NULL)
-  {
+while (*aliases)
   switch(match_check_string(*aliases++, ss, -1, TRUE, TRUE, TRUE, valueptr))
     {
     case OK:    return OK;
     case DEFER: return DEFER;
     }
-  }
 return FAIL;
 }
 
@@ -3078,18 +3207,16 @@ verify_check_this_host(const uschar **listptr, unsigned int *cache_bits,
 int rc;
 unsigned int *local_cache_bits = cache_bits;
 const uschar *save_host_address = deliver_host_address;
-check_host_block cb;
-cb.host_name = host_name;
-cb.host_address = host_address;
+check_host_block cb = { .host_name = host_name, .host_address = host_address };
 
-if (valueptr != NULL) *valueptr = NULL;
+if (valueptr) *valueptr = NULL;
 
 /* If the host address starts off ::ffff: it is an IPv6 address in
 IPv4-compatible mode. Find the IPv4 part for checking against IPv4
 addresses. */
 
-cb.host_ipv4 = (Ustrncmp(host_address, "::ffff:", 7) == 0)?
-  host_address + 7 : host_address;
+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,
@@ -3315,9 +3442,8 @@ else
 
   /* 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.
+  use of A6 records. However, A6 records are no longer supported. Leave the code
+  here, just in case.
 
   Quite apart from one A6 RR generating multiple addresses, there are DNS
   lists that return more than one A record, so we must handle multiple
@@ -3333,25 +3459,23 @@ else
     for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
          rr;
          rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
-      {
       if (rr->type == T_A)
         {
         dns_address *da = dns_address_from_rr(&dnsa, rr);
         if (da)
           {
           *addrp = da;
-          while (da->next != NULL) da = da->next;
-          addrp = &(da->next);
+          while (da->next) da = da->next;
+          addrp = &da->next;
          if (ttl > rr->ttl) ttl = rr->ttl;
           }
         }
-      }
 
     /* If we didn't find any A records, change the return code. This can
     happen when there is a CNAME record but there are no A records for what
     it points to. */
 
-    if (cb->rhs == NULL) cb->rc = DNS_NODATA;
+    if (!cb->rhs) cb->rc = DNS_NODATA;
     }
 
   cb->expiry = time(NULL)+ttl;
@@ -3373,7 +3497,7 @@ if (cb->rc == DNS_SUCCEED)
   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)
+  for (da = cb->rhs->next; da; da = da->next)
     addlist = string_sprintf("%s, %s", addlist, da->address);
 
   HDEBUG(D_dnsbl) debug_printf("DNS lookup for %s succeeded (yielding %s)\n",
@@ -3382,9 +3506,9 @@ if (cb->rc == DNS_SUCCEED)
   /* 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)
+  if (iplist)
     {
-    for (da = cb->rhs; da != NULL; da = da->next)
+    for (da = cb->rhs; da; da = da->next)
       {
       int ipsep = ',';
       uschar ip[46];
@@ -3394,12 +3518,11 @@ if (cb->rc == DNS_SUCCEED)
       /* Handle exact matching */
 
       if (!bitmask)
-        {
-        while ((res = string_nextinlist(&ptr, &ipsep, ip, sizeof(ip))) != NULL)
-          {
-          if (Ustrcmp(CS da->address, ip) == 0) break;
-          }
-        }
+       {
+        while ((res = string_nextinlist(&ptr, &ipsep, ip, sizeof(ip))))
+          if (Ustrcmp(CS da->address, ip) == 0)
+           break;
+       }
 
       /* Handle bitmask matching */
 
@@ -3419,7 +3542,7 @@ if (cb->rc == DNS_SUCCEED)
 
         /* Scan the returned addresses, skipping any that are IPv6 */
 
-        while ((res = string_nextinlist(&ptr, &ipsep, ip, sizeof(ip))) != NULL)
+        while ((res = string_nextinlist(&ptr, &ipsep, ip, sizeof(ip))))
           {
           if (host_aton(ip, address) != 1) continue;
           if ((address[0] & mask) == address[0]) break;
@@ -3452,17 +3575,13 @@ if (cb->rc == DNS_SUCCEED)
         switch(match_type)
           {
           case 0:
-          res = US"was no match";
-          break;
+           res = US"was no match"; break;
           case MT_NOT:
-          res = US"was an exclude match";
-          break;
+           res = US"was an exclude match"; break;
           case MT_ALL:
-          res = US"was an IP address that did not match";
-          break;
+           res = US"was an IP address that did not match"; break;
           case MT_NOT|MT_ALL:
-          res = US"were no IP addresses that did not match";
-          break;
+           res = US"were no IP addresses that did not match"; break;
           }
         debug_printf("=> but we are not accepting this block class because\n");
         debug_printf("=> there %s for %s%c%s\n",
@@ -3494,15 +3613,15 @@ if (cb->rc == DNS_SUCCEED)
       {
       dns_record *rr;
       for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
-           rr != NULL;
+           rr;
            rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
         if (rr->type == T_TXT) break;
-      if (rr != NULL)
+      if (rr)
         {
         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));
+        cb->text = string_sprintf("%.*s", len, CUS (rr->data+1));
         store_pool = old_pool;
         }
       }