[Dshield] Denying incoming email by reverse lookup of ISP DHCP-ed addresses

Stef stefmit at gmail.com
Fri Jun 17 15:46:12 GMT 2005

You all know how some of the ISPs started denying email from what are
home-based accounts, probably by doing a reverse lookup on the
incoming IP, and looking for strings "hinting" on the dynamic nature
of that IP assignment (e.g.

$ dig -x
<snipped irrelevant info>
;; ANSWER SECTION: 6028 IN     PTR    
<snipped irrrelevant info> )

so my question is: does anyone know of a "canned" script, or add-on to
std email servers (sendmail, postfix, etc.), or a standalone third
party solution, with all the potential format of name-addresses like
the above, pre-built - before I start writing my own (perhaps going
after the email header's IP, and doing a reverse lookup of the
original IP, and rejecting the ones where the IP x.y.z.w resoved to a
name containing x-w-z-w ... but I am not sure if this is the rule for
all ISPs)?!?


P.S. The IP address above is real, one of the many already infected
with the Netsky's of the world...

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