[unisog] Rejecting incoming mail with from addresses in your own domain.

Steve VanDevender stevev at darkwing.uoregon.edu
Tue Jul 22 02:24:31 GMT 2003

Russell Fulton writes:
 > The mail that triggered this though was sent to at least one researcher
 > in our medical school and purported to be an advertisement for DNA
 > analysis software.  If one followed the links and  downloaded the trial
 > versions you ended up with some sort of spy ware installed on your
 > system.  The email had a From: header of DNAuser at auckland.ac.nz.  I am
 > also sure that everyone agrees that spammers and worms frequently use
 > From: headers in the recipient's domain to make the message appear more
 > trustworthy.

If someone wants to do this kind of social engineering, they can just as
easily forge a valid domain that isn't yours if you happen to block
incoming mail that is apparently from your domain.

Which thing are you proposing to block on -- the envelope sender
(specified in the SMTP "MAIL From:") or the header sender (in the
"From:" header)?  Either way, you are likely to cause problems for
legitimate off-campus users who are using other ISPs but sending mail
using their university addresses, especially if they can't all use your
SMTP-over-TLS solution (some ISPs block all port 25 connections except
those to their own mail hosts).

I suspect the kind of blocking you are proposing won't buy you much in
the way of real security but will bring you a lot of headaches, and will
be difficult to get right.  There are probably much better measures you
could take to prevent social engineering or mail worm propagation than

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