[unisog] Email and tcpwrappers

Christopher A Bongaarts cab at tc.umn.edu
Mon Apr 21 21:49:06 GMT 2003

As John LaPrad once put it so eloquently:

> We tried requiring rDNS but had to give it up. Many, many legitimate
> emails come from improperly configured servers. We even had some sys
> admins tell us that their security policy required them to have
> bogus rDNS info.

Not sure what they're trying to hide by having "bogus rDNS info"
(whatever that means).  Something as simple as AOL's hexIP.ipt.aol.com 
format can be constructed to reveal no additional information than the 
IP already conveys.

At any rate, our Duluth campus decided to start denying inbound mail
from sites with bad rDNS, and has not seen any major problems.  They
have around 10k users...

For mail that comes through our central systems
(@umn.edu/@tc.umn.edu), we require rDNS on selected networks.  This
gives us quite a bit of spamblocking effectiveness, yet gives us the
flexibility to make exceptions for networks if people complain.
(There's a lot more to our system; it is described in a previous "what 
are you doing to control spam" thread on this list--see archives.)

> ______________________________________________________________________
> John LaPrad, CNE, CCNA, CCDA
> Manager of Network Services
> Saginaw Valley State University
> Phone:  989-964-7134
> Fax:  989-964-7446
> >>> Jenett Tillotson <jtillots at pharmacy.purdue.edu> 04/14/03 09:48AM >>>
> I was wondering if anyone had some good advice about how to deal with 
> machines that don't have a DNS reverse lookup and port 25.  Since we are 
> getting a lot of pornographic email from machines which aren't registered, 
> I'm hoping to block email from machines that don't have a reverse lookup.  
> However, in doing some initial checking on this, it appears that A LOT of 
> machines sending legitimate email do not have a reverse lookup.
> What are other people doing out there to stop the barrage of pornographic 
> email?  
> Thanks in advance,
> Jenett Tillotson
> School of Pharmacy
> Purdue University
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