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Redirecting SMTP

Thu Aug 24, 2006 9:54 am

I have a slight problem. I have a wireless customer with 2 internet connections, one of them ours, another is a cable company. Currently, we are their backup connection so the default route is to the cable modem. We provide their email, web and anti-spam services. It recently came to my attention they are sending all their mail via the cable provider's SMTP, which prevents our Anti-Spam Proxy from identifying "good" senders. There's over 90 computers, most of them have Deep Freeze on them, so making the change would be difficult at best. I have thought of several solutions:

1. Since they use MT for DNS relay, set a static DNS entry for the cable provider's SMTP server to point to mine.
2. Use a NAT rule (I tried all TCP 25 to DST-NAT my SMTP IP address).

The problem is slightly complicated beyond that. My SMTP server is on a different subnet than their wireless IP, so without a special policy route, it ends up going to my network the wrong way anyhow. I tried both of the above ideas, just to find that for some reason I can ping the server, but can't telnet to port 25 or visit the web mail.
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Thu Aug 24, 2006 6:14 pm

Rule 2 should work, you just need to make sure the traffic has a path back to them ... from the mail server can you reach the client ip subnet? Packets might be getting there but not making it back or something.

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Thu Aug 24, 2006 8:03 pm

Sounds like you need to use a route rule to set it straight. ChangeIP is correct, you should use method #2 though I would specify a destination IP in your rules so you dont snag everyone (unless that is what you want).

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