This patch enables tarpitting for rblsmtpd from the ucspi-tcp-0.88 package.
Use -t <seconds> to set the maximum tarpitting time. It writes a message 
like "host 1.2.3.4 tarpitted for 3600 seconds" to stderr.
http://www.wolfermann.org/djbware.html

--- rblsmtpd.c.orig	10 Feb 2003 09:00:43 -0000
+++ rblsmtpd.c	4 Jun 2004 15:13:30 -0000
@@ -99,11 +99,46 @@
 char inspace[64]; buffer in = BUFFER_INIT(read,0,inspace,sizeof inspace);
 char outspace[1]; buffer out = BUFFER_INIT(write,1,outspace,sizeof outspace);
 
-void reject() { buffer_putflush(&out,message.s,message.len); }
+static int startpit;
+void logpit()
+{
+	buffer_puts(buffer_2,"rblsmtpd: ");
+	buffer_puts(buffer_2,"host ");
+	buffer_puts(buffer_2,ip_env);
+	buffer_puts(buffer_2," tarpitted for ");
+	buffer_put(buffer_2,strnum,fmt_ulong(strnum,(int)time() - startpit));
+	buffer_puts(buffer_2," seconds");
+	buffer_puts(buffer_2,"\n");
+	buffer_flush(buffer_2);
+}
+
+void reject()
+{
+	startpit = (int)time();
+	message.s[3] = '-';
+	buffer_putflush(&out,message.s,message.len);
+	message.s[4] = '\r';
+	message.s[5] = '\n';
+	message.len = 6;
+	while(1) {
+		buffer_putflush(&out,message.s,message.len);
+		sleep(10);
+	}
+}
+
 void accept() { buffer_putsflush(&out,"250 rblsmtpd.local\r\n"); }
 void greet()  { buffer_putsflush(&out,"220 rblsmtpd.local\r\n"); }
-void quit()   { buffer_putsflush(&out,"221 rblsmtpd.local\r\n"); _exit(0); }
-void drop()   { _exit(0); }
+void quit()
+{
+	buffer_putsflush(&out,"221 rblsmtpd.local\r\n"); 
+	logpit();
+	_exit(0);
+}
+void drop()
+{
+	logpit();
+	_exit(0);
+}
 
 struct commands smtpcommands[] = {
   { "quit", quit, 0 }
@@ -146,6 +181,7 @@
     reject();
   else {
     sig_catch(sig_alarm,drop);
+    sig_catch(sig_pipe,drop);
     alarm(timeout);
     greet();
     commands(&in,smtpcommands);