diff -ur exim-3.22-orig/src/accept.c exim-3.22/src/accept.c
--- exim-3.22-orig/src/accept.c	Wed Jun 20 13:37:19 2001
+++ exim-3.22/src/accept.c	Wed Jun 20 13:34:43 2001
@@ -1523,6 +1523,30 @@
     (header_names != header_names_normal && resentmsgid_header == NULL))
   {
   BOOL use_default = TRUE;
+  /* use primary_hostname or message_id_domain for domain-part 
+   * of Message-ID */
+  char *my_message_id_domain;
+  if (message_id_domain != NULL)
+    {
+    my_message_id_domain = expand_string(message_id_domain);
+    if (my_message_id_domain != 0)
+      {
+      if (*my_message_id_domain != 0)
+        {
+        uschar *ee;
+        for (ee = (uschar *)my_message_id_domain; *ee != 0; ee++)
+           /* Accept only a-z A-Z - and .
+            * 45 is -, 122 is z */
+          if ((*ee) < 45 || (*ee) > 122 || strchr("/<>;:?=@[]\\^_`", (*ee)) != NULL) *ee = '-';
+        }
+      }
+    else
+      log_write(0, LOG_MAIN|LOG_PANIC,
+        "expansion of \"%s\" (message_id_header_domain) "
+        "failed: %s", message_id_domain, expand_string_message);
+    }
+  else
+    my_message_id_domain=primary_hostname;
   if (message_id_text != NULL)
     {
     char *e = expand_string(message_id_text);
@@ -1534,7 +1558,7 @@
         for (ee = (uschar *)e; *ee != 0; ee++)
           if (mac_iscntrl_or_special(*ee)) *ee = '-';
         header_add(htype_id, "%s: <%s.%s@%s>\n", header_names[hn_msgid].name,
-          message_id_external, e, primary_hostname);
+          message_id_external, e, my_message_id_domain);
         use_default = FALSE;
         }
       }
@@ -1545,7 +1569,7 @@
     }
   if (use_default)
     header_add(htype_id, "%s: <%s@%s>\n", header_names[hn_msgid].name,
-      message_id_external, primary_hostname);
+      message_id_external, my_message_id_domain);
   }
 
 /* Ensure the recipients list is fully qualified and rewritten. If we
diff -ur exim-3.22-orig/src/globals.c exim-3.22/src/globals.c
--- exim-3.22-orig/src/globals.c	Fri Jan 19 10:32:08 2001
+++ exim-3.22/src/globals.c	Wed Jun 20 13:00:58 2001
@@ -452,6 +452,7 @@
 uid_t  message_filter_uid     = 0;
 BOOL   message_filter_uid_set = FALSE;
 char  *message_id;
+char  *message_id_domain      = NULL;
 char  *message_id_text        = NULL;
 char   message_id_option[MESSAGE_ID_LENGTH + 3];
 char  *message_id_external;
diff -ur exim-3.22-orig/src/globals.h exim-3.22/src/globals.h
--- exim-3.22-orig/src/globals.h	Fri Jan 19 10:32:08 2001
+++ exim-3.22/src/globals.h	Wed Jun 20 13:00:58 2001
@@ -329,6 +329,7 @@
 extern char   message_id_option[];    /* -E<message-id> for use as option */
 extern char  *message_id_external;    /* External form of following */
 extern char  *message_id;             /* Internal id of message being handled */
+extern char  *message_id_domain;      /* message_id domain-part */
 extern char  *message_id_text;        /* Expanded to form message_id */
 extern int    message_linecount;      /* As it says */
 extern FILE  *message_log;            /* Open message log while delivering */
diff -ur exim-3.22-orig/src/readconf.c exim-3.22/src/readconf.c
--- exim-3.22-orig/src/readconf.c	Wed Jun 20 13:36:14 2001
+++ exim-3.22/src/readconf.c	Wed Jun 20 13:00:58 2001
@@ -144,6 +144,7 @@
   { "message_filter_pipe_transport",opt_stringptr,&message_filter_pipe_transport },
   { "message_filter_reply_transport",opt_stringptr,&message_filter_reply_transport },
   { "message_filter_user",      opt_uid,         &message_filter_uid },
+  { "message_id_header_domain",   opt_stringptr,   &message_id_domain },
   { "message_id_header_text",   opt_stringptr,   &message_id_text },
   { "message_size_limit",       opt_mkint,       &message_size_limit },
   { "message_size_limit_count_recipients", opt_bool, &message_size_limit_count_recipients },