diff -u smail-3.2.0.102.orig/src/config.c smail-3.2.0.102/src/config.c
--- smail-3.2.0.102.orig/src/config.c	Sat Apr 11 17:30:13 1998
+++ smail-3.2.0.102/src/config.c	Sat Aug 22 11:44:45 1998
@@ -28,6 +28,7 @@
 #endif
 
 char *listen_name = NULL; 		/* DNS name of interface to listen on */
+char *rbl_domain = NULL; 		/* DNS domain for RBL lockout */
 char *visible_name = VISIBLE_NAME;	/* hostname used in outgoing addrs */
 char *visible_domains = VISIBLE_DOMAINS; /* domain used in outgoing headers */
 char *uucp_name = UUCP_NAME;		/* hostname used in !-routes */
diff -u smail-3.2.0.102.orig/src/extern.h smail-3.2.0.102/src/extern.h
--- smail-3.2.0.102.orig/src/extern.h	Sun Feb 15 14:12:33 1998
+++ smail-3.2.0.102/src/extern.h	Sat Aug 22 11:52:04 1998
@@ -25,6 +25,7 @@
 
 /* external variables defined in config.c */
 extern char *listen_name;		/* DNS name of interface to listen on */
+extern char *rbl_domain;                /* DNS name for RBL lockout */
 extern char *visible_name;		/* hostname used in outgoing addrs */
 extern char *visible_domains;		/* domain used in outgoing headers */
 extern char *uucp_name;			/* hostname used in !-routes */
diff -u smail-3.2.0.102.orig/src/smailconf.c smail-3.2.0.102/src/smailconf.c
--- smail-3.2.0.102.orig/src/smailconf.c	Sat Oct 18 08:57:54 1997
+++ smail-3.2.0.102/src/smailconf.c	Sat Aug 22 11:44:45 1998
@@ -91,6 +91,7 @@
     { "hostnames", t_string, NULL, (tup *)&hostnames, 0 },
     { "hostname", t_string, NULL, (tup *)&hostnames, 0 },
     { "listen_name", t_string, NULL, (tup *)&listen_name, 0 },
+    { "rbl_domain", t_string, NULL, (tup *)&rbl_domain, 0 },
     { "lock_by_name", t_boolean, NULL, (tup *)&lock_by_name, 0 },
     { "lock_mode", t_mode, NULL, (tup *)&lock_mode, 0 },
     { "log_mode", t_mode, NULL, (tup *)&log_mode, 0 },
diff -u smail-3.2.0.102.orig/src/smtprecv.c smail-3.2.0.102/src/smtprecv.c
--- smail-3.2.0.102.orig/src/smtprecv.c	Sun Jun  7 19:02:07 1998
+++ smail-3.2.0.102/src/smtprecv.c	Sat Aug 22 11:54:20 1998
@@ -207,6 +207,9 @@
     struct sockaddr_in from_sa;
     int from_sa_len = sizeof(from_sa);
     struct hostent *shp = NULL;		/* result of gethostbyaddr() */
+	char *rbl_addr;
+	char rbl_host[128];
+	struct hostent *rbl_p = NULL;
 
 # ifndef OBSOLETE_RESOLVER
     extern int h_errno;			/* import h_errno; many systems don't define it in <netdb.h> */
@@ -324,7 +327,28 @@
 	   sender_host_addr ? sender_host_addr : "<unset>",
 	   sender_host_really ? sender_host_really : "<unknown>",
 	   smtp_local_net ? smtp_local_net : "<unset>");
+
+	if (sender_host_addr && rbl_domain) {
+    	rbl_addr = (unsigned char *)&from_sa.sin_addr;
+
+    	sprintf(rbl_host, "%d.%d.%d.%d.%s",
+        	rbl_addr[3] & 0xff,
+         	rbl_addr[2] & 0xff,
+         	rbl_addr[1] & 0xff,
+        	rbl_addr[0] & 0xff,
+			rbl_domain);
+ 
+		if ((rbl_p = gethostbyname(rbl_host)) != NULL) {
+			fprintf(out, "550 You are not permitted to send mail - %s\r\n",
+				rbl_host);
+			fflush(out);
+			write_log(WRITE_LOG_SYS, "connection refused from %s because of RBL",
+				inet_ntoa(from_sa.sin_addr));
+			smtp_sig_unlink(1);
+		}		
+}
 #endif /* HAVE_BSD_NETWORKING */
+  
 
     /* Set the protocol used - this used to be in the HELO code, but that gives
      * problems if the sender never says HELO