anti-relay patches

Last Update 1997-05-16
Newsgroups: comp.mail.sendmail
From: (Kim)
Subject: Patches for filtering on email src/dest IP addresses - anti-relay patches
Message-ID: <>
Summary:  email relay IP filtering no-spam
Date: Fri, 16 May 1997 14:48:19 GMT

I've gotten enough requests for the patches I have made to sendmail 8.8.5
to filter email that I have put them up on my ftp site here at netcom.

What these patches do is to allow sendmail to detect if email came from
a source 'outside' a set of IP network addresses, and is also destined
for 'outside' - i.e. someone is trying to relay email off of your server.

The second of the patches adds some additional functionality to,
allowing you to do more filtering based on IP addresses and CIDR blocks
in  (The current check_rcpt I have seen would only let you
check against IP address by class C block as far as I can tell, so if
you wanted to block against a CIDR block of 32 class C addresses, you
would have to enter all 32 class Cs to be blocked.  This patch allows
you to block by IP network and netmask, so it becomes easier to block
email from entire CIDR blocks.)

These are pretty rough patches.  Use them at your own risk.  The README
files contain some basic information on what the patches do and what
their problems are.

Please let me know if you find these useful - I'm still poking at them
in my brief moments of spare time.  :)

Read the README files!  There are two separate patches in there for two 
separate filtering methods.

Cheers, and good luck.

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Claus Aßmann Please send comments to: <>