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.