diff -Nur sendmail-8.12.0.orig/sendmail/collect.c sendmail-8.12.0/sendmail/collect.c
--- sendmail-8.12.0.orig/sendmail/collect.c	Wed Sep  5 00:43:02 2001
+++ sendmail-8.12.0/sendmail/collect.c	Mon Sep 24 10:25:42 2001
@@ -15,6 +15,8 @@
 
 SM_RCSID("@(#)$Id$")
 
+#define MAXHDRZ 512
+
 static void	collecttimeout __P((time_t));
 static void	dferror __P((SM_FILE_T *volatile, char *, ENVELOPE *));
 static void	eatfrom __P((char *volatile, ENVELOPE *));
@@ -292,6 +294,7 @@
 	HDR **hdrp;
 	register ENVELOPE *e;
 {
+	int hdrz = 0;
 	register SM_FILE_T *volatile df;
 	volatile bool ignrdot;
 	volatile time_t dbto;
@@ -582,6 +585,16 @@
 				mstate = MS_BODY;
 				goto nextstate;
 			}
+ 
+            if (hdrz++>MAXHDRZ)
+                        {
+                                sm_syslog(LOG_NOTICE, e->e_id,
+                                "excessive headers from %s during message collect",
+                                CurHostName ? CurHostName : "<local machine>");
+                                errno = 0;
+                                usrerr("451 Stop this. You are lame.");
+                                goto readerr;
+                        }
 
 			/* check for possible continuation line */
 			do