diff -bru postfix-2.0.18/src/global/mail_params.c postfix-2.0.18-sender_relay/src/global/mail_params.c
--- postfix-2.0.18/src/global/mail_params.c	2002-12-13 23:04:31.000000000 +0100
+++ postfix-2.0.18-sender_relay/src/global/mail_params.c	2004-02-01 00:49:27.000000000 +0100
@@ -165,6 +165,7 @@
 char   *var_myorigin;
 char   *var_mydest;
 char   *var_relayhost;
+char   *var_relayhost_map;
 char   *var_transit_origin;
 char   *var_transit_dest;
 char   *var_mail_name;
@@ -433,6 +434,7 @@
 	VAR_MYDEST, DEF_MYDEST, &var_mydest, 0, 0,
 	VAR_MYORIGIN, DEF_MYORIGIN, &var_myorigin, 1, 0,
 	VAR_RELAYHOST, DEF_RELAYHOST, &var_relayhost, 0, 0,
+	VAR_RELAYHOST_MAP, DEF_RELAYHOST_MAP, &var_relayhost_map, 0, 0,
 	VAR_PROGRAM_DIR, DEF_PROGRAM_DIR, &var_program_dir, 1, 0,
 	VAR_DAEMON_DIR, DEF_DAEMON_DIR, &var_daemon_dir, 1, 0,
 	VAR_COMMAND_DIR, DEF_COMMAND_DIR, &var_command_dir, 1, 0,
diff -bru postfix-2.0.18/src/global/mail_params.h postfix-2.0.18-sender_relay/src/global/mail_params.h
--- postfix-2.0.18/src/global/mail_params.h	2003-03-03 23:07:03.000000000 +0100
+++ postfix-2.0.18-sender_relay/src/global/mail_params.h	2004-02-01 01:03:34.000000000 +0100
@@ -165,6 +165,10 @@
 #define DEF_RELAYHOST		""
 extern char *var_relayhost;
 
+#define VAR_RELAYHOST_MAP	"relayhost_map"
+#define DEF_RELAYHOST_MAP	""
+extern char *var_relayhost_map;
+
 #define VAR_FALLBACK_RELAY	"fallback_relay"
 #define DEF_FALLBACK_RELAY	""
 extern char *var_fallback_relay;
diff -bru postfix-2.0.18/src/global/resolve_clnt.h postfix-2.0.18-sender_relay/src/global/resolve_clnt.h
--- postfix-2.0.18/src/global/resolve_clnt.h	2002-12-08 17:45:58.000000000 +0100
+++ postfix-2.0.18-sender_relay/src/global/resolve_clnt.h	2004-02-04 17:33:10.000000000 +0100
@@ -31,6 +31,7 @@
 #define RESOLVE_CLASS_VIRTUAL	(1<<10)	/* virtual_mailbox_domains */
 #define RESOLVE_CLASS_RELAY	(1<<11)	/* relay_domains */
 #define RESOLVE_CLASS_DEFAULT	(1<<12)	/* raise reject_unauth_destination */
+#define RESOLVE_CLASS_SMARTHOST (1<<13) /* delivery via smarthost choosen */
 
 #define RESOLVE_CLASS_FINAL \
 	(RESOLVE_CLASS_LOCAL | RESOLVE_CLASS_ALIAS | RESOLVE_CLASS_VIRTUAL)
diff -bru postfix-2.0.18/src/qmgr/qmgr.c postfix-2.0.18-sender_relay/src/qmgr/qmgr.c
--- postfix-2.0.18/src/qmgr/qmgr.c	2002-12-22 20:31:18.000000000 +0100
+++ postfix-2.0.18-sender_relay/src/qmgr/qmgr.c	2004-02-04 18:10:36.000000000 +0100
@@ -288,6 +288,8 @@
 static QMGR_SCAN *qmgr_incoming;
 static QMGR_SCAN *qmgr_deferred;
 
+MAPS   *relayhost_map;
+
 /* qmgr_deferred_run_event - queue manager heartbeat */
 
 static void qmgr_deferred_run_event(int unused_event, char *dummy)
@@ -431,6 +433,15 @@
     }
 }
 
+/* qmgr_pre_init - pre-jail initialization */
+
+static void qmgr_pre_init(char *unused_name, char **unused_argv)
+{
+    relayhost_map = *var_relayhost_map ?
+	maps_create("relayhosts", var_relayhost_map, DICT_FLAG_LOCK) :
+	0;
+}
+
 /* qmgr_post_init - post-jail initialization */
 
 static void qmgr_post_init(char *unused_name, char **unused_argv)
@@ -511,6 +522,7 @@
 			MAIL_SERVER_STR_TABLE, str_table,
 			MAIL_SERVER_BOOL_TABLE, bool_table,
 			MAIL_SERVER_TIME_TABLE, time_table,
+			MAIL_SERVER_PRE_INIT, qmgr_pre_init,
 			MAIL_SERVER_POST_INIT, qmgr_post_init,
 			MAIL_SERVER_LOOP, qmgr_loop,
 			MAIL_SERVER_PRE_ACCEPT, pre_accept,
diff -bru postfix-2.0.18/src/qmgr/qmgr.h postfix-2.0.18-sender_relay/src/qmgr/qmgr.h
--- postfix-2.0.18/src/qmgr/qmgr.h	2002-12-08 02:19:01.000000000 +0100
+++ postfix-2.0.18-sender_relay/src/qmgr/qmgr.h	2004-02-04 18:13:33.000000000 +0100
@@ -15,6 +15,11 @@
 #include <scan_dir.h>
 
  /*
+  * Global library.
+  */
+#include <maps.h>
+
+ /*
   * The queue manager is built around lots of mutually-referring structures.
   * These typedefs save some typing.
   */
@@ -307,6 +312,11 @@
 extern void qmgr_scan_request(QMGR_SCAN *, int);
 extern char *qmgr_scan_next(QMGR_SCAN *);
 
+ /*
+  * qmgr.c
+  */
+extern MAPS *relayhost_map;
+
 /* LICENSE
 /* .ad
 /* .fi
diff -bru postfix-2.0.18/src/qmgr/qmgr_message.c postfix-2.0.18-sender_relay/src/qmgr/qmgr_message.c
--- postfix-2.0.18/src/qmgr/qmgr_message.c	2003-04-11 15:19:51.000000000 +0200
+++ postfix-2.0.18-sender_relay/src/qmgr/qmgr_message.c	2004-02-05 00:20:01.000000000 +0100
@@ -569,6 +569,20 @@
 	}
 
 	/*
+	 * Selected the proper server on basis of the sender's adress,
+	 * if a smarthost was resolved as next hop.
+	 */
+	if (relayhost_map && (reply.flags & RESOLVE_CLASS_SMARTHOST)) {
+	    const char * smarthost;
+
+	    if (smarthost = maps_find(relayhost_map, message->sender, 0)) {
+		msg_info("using smart host %s for sender %s",
+			 smarthost, message->sender);
+		vstring_strcpy(reply.nexthop, smarthost);
+	    }
+        }
+
+	/*
 	 * XXX The nexthop destination is also used as lookup key for the
 	 * per-destination queue. Fold the nexthop to lower case so that we
 	 * don't have multiple queues for the same site.
diff -bru postfix-2.0.18/src/trivial-rewrite/resolve.c postfix-2.0.18-sender_relay/src/trivial-rewrite/resolve.c
--- postfix-2.0.18/src/trivial-rewrite/resolve.c	2003-01-12 00:52:41.000000000 +0100
+++ postfix-2.0.18-sender_relay/src/trivial-rewrite/resolve.c	2004-02-04 18:28:25.000000000 +0100
@@ -459,12 +459,14 @@
 	    /*
 	     * With off-host delivery, relayhost overrides recipient domain.
 	     */
-	    if (*var_relayhost)
+            if (*var_relayhost) {
 		vstring_strcpy(nexthop, var_relayhost);
-	    else
+                *flags |= RESOLVE_CLASS_SMARTHOST;
+            } else {
 		vstring_strcpy(nexthop, rcpt_domain);
 	}
     }
+    }
 
     /*
      * Local delivery.