diff -ruN qmail-1.03.orig/Makefile qmail-1.03/Makefile
--- qmail-1.03.orig/Makefile	Mon Jun 15 12:53:16 1998
+++ qmail-1.03/Makefile	Thu May  6 13:02:37 1999
@@ -1536,13 +1536,13 @@
 timeoutwrite.o ip.o ipme.o ipalloc.o control.o constmap.o received.o \
 date822fmt.o now.o qmail.o cdb.a fd.a wait.a datetime.a getln.a \
 open.a sig.a case.a env.a stralloc.a alloc.a substdio.a error.a str.a \
-fs.a auto_qmail.o socket.lib
+fs.a auto_qmail.o socket.lib dns.o dns.lib
 	./load qmail-smtpd rcpthosts.o commands.o timeoutread.o \
 	timeoutwrite.o ip.o ipme.o ipalloc.o control.o constmap.o \
 	received.o date822fmt.o now.o qmail.o cdb.a fd.a wait.a \
 	datetime.a getln.a open.a sig.a case.a env.a stralloc.a \
 	alloc.a substdio.a error.a str.a fs.a auto_qmail.o  `cat \
-	socket.lib`
+	socket.lib` dns.o `cat dns.lib`
 
 qmail-smtpd.0: \
 qmail-smtpd.8
diff -ruN qmail-1.03.orig/qmail-control.9 qmail-1.03/qmail-control.9
--- qmail-1.03.orig/qmail-control.9	Mon Jun 15 12:53:16 1998
+++ qmail-1.03/qmail-control.9	Thu May  6 13:00:45 1999
@@ -55,6 +55,7 @@
 .I idhost	\fIme	\fRqmail-inject
 .I localiphost	\fIme	\fRqmail-smtpd
 .I locals	\fIme	\fRqmail-send
+.I mfcheck	\fR0	\fRqmail-smtpd
 .I morercpthosts	\fR(none)	\fRqmail-smtpd
 .I percenthack	\fR(none)	\fRqmail-send
 .I plusdomain	\fIme	\fRqmail-inject
diff -ruN qmail-1.03.orig/qmail-smtpd.8 qmail-1.03/qmail-smtpd.8
--- qmail-1.03.orig/qmail-smtpd.8	Mon Jun 15 12:53:16 1998
+++ qmail-1.03/qmail-smtpd.8	Thu May  6 12:12:31 1999
@@ -97,6 +97,12 @@
 This is done before
 .IR rcpthosts .
 .TP 5
+.I mfcheck
+If set,
+.B qmail-smtpd
+tries to resolve the domain of the envelope from address.  It can be
+handy when you want to filter out spamhosts.
+.TP 5
 .I morercpthosts
 Extra allowed RCPT domains.
 If
diff -ruN qmail-1.03.orig/qmail-smtpd.c qmail-1.03/qmail-smtpd.c
--- qmail-1.03.orig/qmail-smtpd.c	Mon Jun 15 12:53:16 1998
+++ qmail-1.03/qmail-smtpd.c	Wed Jun 16 12:48:21 1999
@@ -23,9 +23,11 @@
 #include "timeoutread.h"
 #include "timeoutwrite.h"
 #include "commands.h"
+#include "dns.h"
 
 #define MAXHOPS 100
 unsigned int databytes = 0;
+unsigned int mfchk = 0;
 int timeout = 1200;
 
 int safewrite(fd,buf,len) int fd; char *buf; int len;
@@ -50,6 +52,8 @@
 void straynewline() { out("451 See http://pobox.com/~djb/docs/smtplf.html.\r\n"); flush(); _exit(1); }
 
 void err_bmf() { out("553 sorry, your envelope sender is in my badmailfrom list (#5.7.1)\r\n"); }
+void err_hmf() { out("553 sorry, your envelope sender domain must exist (#5.7.1)\r\n"); }
+void err_smf() { out("451 DNS temporary failure (#4.3.0)\r\n"); }
 void err_nogateway() { out("553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)\r\n"); }
 void err_unimpl() { out("502 unimplemented (#5.5.1)\r\n"); }
 void err_syntax() { out("555 syntax error (#5.5.4)\r\n"); }
@@ -112,6 +116,10 @@
 
   if (rcpthosts_init() == -1) die_control();
 
+  if (control_readint(&mfchk,"control/mfcheck") == -1) die_control();
+  x = env_get("MFCHECK");
+  if (x) { scan_ulong(x,&u); mfchk = u; }
+
   bmfok = control_readfile(&bmf,"control/badmailfrom",0);
   if (bmfok == -1) die_control();
   if (bmfok)
@@ -208,6 +216,25 @@
   return 0;
 }
 
+int mfcheck()
+{
+  stralloc sa = {0};
+  ipalloc ia = {0};
+  unsigned int random;
+  int j;
+
+  if (!mfchk) return 0;
+  random = now() + (getpid() << 16);
+  j = byte_rchr(addr.s,addr.len,'@') + 1;
+  if (j < addr.len) {
+    stralloc_copys(&sa, addr.s + j);
+    dns_init(0);
+    j = dns_mxip(&ia,&sa,random);
+    if (j < 0) return j;
+  }
+  return 0;
+}
+
 int addrallowed()
 {
   int r;
@@ -241,6 +268,11 @@
 {
   if (!addrparse(arg)) { err_syntax(); return; }
   flagbarf = bmfcheck();
+  switch(mfcheck()) {
+    case DNS_HARD: err_hmf(); return;
+    case DNS_SOFT: err_smf(); return;
+    case DNS_MEM: die_nomem();
+  }
   seenmail = 1;
   if (!stralloc_copys(&rcptto,"")) die_nomem();
   if (!stralloc_copys(&mailfrom,addr.s)) die_nomem();