From 8ebb34bd4f4328f7828735be480d77f884f9359a Mon Sep 17 00:00:00 2001
From: John Denker <jsd@av8n.com>
Date: Sun, 3 Jun 2012 21:25:41 -0700
Subject: Reject emails addressed to multiple recipients with a null envelope
 sender. A lot of your spam will be arriving with a null envelope sender. When
 those spam messages have multiple envelope recipients, they cannot be bounce
 messages.

---
 qmail-smtpd.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/qmail-smtpd.c b/qmail-smtpd.c
index 1064008..8c88c4b 100644
--- a/qmail-smtpd.c
+++ b/qmail-smtpd.c
@@ -62,6 +62,7 @@ void err_bmf() { out("553 sorry, your envelope sender is in my badmailfrom list
 void err_nogateway() { out("553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)\r\n"); }
 void err_unimpl(arg) char *arg; { out("502 unimplemented (#5.5.1)\r\n"); }
 void err_syntax() { out("555 syntax error (#5.5.4)\r\n"); }
+void err_relay() { out("553 we don't relay (#5.7.1)\r\n"); }
 void err_wantmail() { out("503 MAIL first (#5.5.1)\r\n"); }
 void err_wantrcpt() { out("503 RCPT first (#5.5.1)\r\n"); }
 void err_noop(arg) char *arg; { out("250 ok\r\n"); }
@@ -237,6 +238,21 @@ int addrallowed()
   return r;
 }
 
+int addrrelay()
+{
+  int j;
+  j = addr.len;
+  while(--j >= 0)
+    if (addr.s[j] == '@') break;
+  if (j < 0) j = addr.len;
+  while(--j >= 0) {
+    if (addr.s[j] == '@') return 1;
+    if (addr.s[j] == '%') return 1;
+    if (addr.s[j] == '!') return 1;
+  }
+  return 0;
+}
+
 
 int seenmail = 0;
 int flagbarf; /* defined if seenmail */
@@ -283,6 +299,7 @@ void smtp_mail(arg) char *arg;
 void smtp_rcpt(arg) char *arg; {
   if (!seenmail) { err_wantmail(); return; }
   if (!addrparse(arg)) { err_syntax(); return; }
+  if (addrrelay()) { err_relay(); return; }
   if (flagbarf) { err_bmf(); return; }
   if (relayclient) {
     --addr.len;
-- 
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