Mailing List Message #6548
From: Bill Cole <>
Subject: Re: Anti-Spam Problems
Date: Wed, 19 Jul 2000 00:27:47 -0400
To: SIMS Discussions <>
At 8:55 PM -0400 7/17/00, Peter Jones @ Jonesfam  imposed structure on a
stream of electrons, yielding:
>Tod: Thanks for the input. Based on your note, I added my _external_ IP
>address to the "Client Hosts" window and now mail flows normally. That is,
>the "relayable" client hosts are
>(The second line wasn't there before, and it's my "external" world [public]
>IP address.)
>I'm not sure why it works, but it does, and I'm not complaining!

This was probably necessary because your client is using some name to get
to the  SIMS server that resolves to the outside address, and as a result
it is routing packets out through a NAT interface and back in to get to
the SIMS server. This is actually rather inefficient and might fail in
some cases where the NAT handler can't handle the tight loop (oddly
enough, IPNR never failed on this but my FlowPoint 2200 router does), and
you might want to look at your client config and/or DNS to help it out.

As an example of how you can fix this is my config. My internal clients
point at '' as the SMTP and POP3 server, and that
name resolves to an internal (192.168.x.x) address, so the clients don't
hit the NAT to talk internally. If I pointed them at the name used for my
MX record ( they would send packets to the public
address that name resolves to. In doing so those packets would pass
through my router's NAT, immediately pass back inside, and they would look
to the SIMS server as if they came from the outside address of the router.
While this might be a way to test my router and ethernet with one machine,
it doesn't actually work very well.

Bill Cole
MAPS L.L.C. Consulting Services Group (work) (personal)
Subscribe (FEED) Subscribe (DIGEST) Subscribe (INDEX) Unsubscribe Mail to Listmaster