[Mimedefang] example of DNS sanity-checking

[Kees Cook]

I saw a few posts to the list asking about details on various DNS tests, 
etc, and I thought I'd share what I wrote.  This was originally part of a 
DNS RBL server I was writing, and it fits nicely into mimedefang too.  I 
haven't broken it out into a separate module yet (which should be pretty 
easy), but it's quite configurable as it is.

The attached mimedefang-filter was originally the base example, but I've 
made a few minor tweaks to the SpamAssassin stuff too (more headers like 
native SpamAssassin, bouncing high scorers, etc).

The big hash at the top of the file has a whole mess of tests for 
rejecting connections (during filter_relay) based on regular expressions.  
This is much nicer than sendmail's access.db stuff, I think.  Also, there 
is DNS spoof checking, and some basic HELO spoof testing (somewhat 
inspired by the filter_relay details in the mimedefang FAQ).

I hope other people using "-r" can use this stuff!  :)

-- 
Kees Cook
Open Souce Development Lab
kees at osdl.org