[Volunteers] list violation: "ShmooCon 2006" announcement

Rick Moen rick at linuxmafia.com
Sun Sep 11 13:03:00 PDT 2005


Quoting Chris Verges (chverges at cisco.com):

> Can we do any kind of reverse-domain verification in sendmail on the 
> svlug mail servers?  Or some kind of anti-spam checking procedures?

Technically, Exim4, rather than sendmail:

  corleone:~ rick$ telnet svlug.org smtp
  Trying 216.218.255.178...
  Connected to svlug.org.
  Escape character is '^]'.
  220 svlug.org ESMTP Exim 4.44 #1 Sun, 11 Sep 2005 12:50:26 -0700 - mm9
  quit
  221 svlug.org closing connection
  Connection closed by foreign host.

One can configure Exim4 to check SPF records (validating return path,
and thus by intention validating the envelope sender).  SPF RRs in a
domain's DNS are in effect reverse MX records, being to MXes what PTR
records are to A records.

Anyhow, one can run Perl library spfd (Mail::SPF::Query) as a daemon and
use Exim4 ACLs like this one to make Exim4 check SPF:
http://spf.pobox.com/exim4.spf.acl-2.09.txt

Last time I tried that on my own MTA, it produced some undesirable
side-effects, but that was quite a long time ago.





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