ISPs blocking SMTP connections from dynamic IP address space

Jerry Bell jerry at
Fri Aug 8 12:47:07 PDT 2003

The problem with running an MTA on a "dynamic IP" is even a little more
difficult than just dealing with the dnsbls.  A while back on the exim users
was a discussion about how technically, the HELO address, forward dns and
reverse dns should all match according to the smtp rfc.  I'm not advocating
one way or the other, but it brings up a good point - that the best way to
run an MTA on a dsl or cable line is to either reflect off your ISP's mail
server (unpopular as per the discussion so far) or to reflect off of some
other 'legitimate' mail server, which is what I do.  I'm fortunate enough to
have a box on a colo network, so I'm able to control the server that my mail
gets reflected off of, but I don't think that's the case for many people.
What may be an option is to look for some form of ISP who provides that
services and gives some control and visibility into the email flow.  I'm not
sure that that exists, but it can't be an expensive service to run (I see a
business opportunity :)

I think it really stinks that it has come to the point that people &
companies have to take such steps to block "dynamic IP's", but I can see
both sides of the arguement.


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