I have yet another customer that is running GroupWise 5x that is getting attacked by some asian spammer trying to dictionary attack Yahoo.co.jp and other regional sites. Until they can get onto GroupWise 6 (which will reject at the SMTP envelope), my recommendation was for them to install a new router capable of limiting port 25 to just my server's IP, the only problem is that he needs something fast and cheap.
Does anyone know of any cheap, chain store stocked routers that are capable of limiting a particular port to a particular IP on inbound only (it still has to deliver by SMTP, just only receive from my IP)? I figure that the following are the best candidates based on the fact that they are readily available.
This may be a bit of overkill for this particular application, but check out SmoothWall (http://www.smoothwall.org). It's a hardened Linux installation, but has been made easy to manage for Linux-phobes like me. The price is right (free), and it runs on any old 486/low end pentium you've got lying around. Takes about 20 minutes to install. In the "port forwarding" page, you can specify that connections from a specific address, on a specific port, should get forwarded. (i.e., port 25 traffic only from your server gets through).
Most of the firewall stuff can be configured via web browser, including blocking a specific IP address. About an hour of surfing on their BBS, and I figured out how to get to a lower level config file that gives me greater granularity over allow/block rules, but for your immediate need, The GUI stuff will probably be enough.
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