I've started to get strage errors in Outlook (after working fine for the last couple of weeks, and with no configuration changes). Further investigation showed that I can't create connections to port 110 or port 25, but other computers on the same network can.
This seems like a classic firewall problem, except that I'm not running anything more than the built-in windows one (and the router's firewall is obviously set up properly, since other computers can do this).
I'd had this problem before (2003), and I can't for the life of me recall how I solved it.
This is one of those things that are just annoying, and the #1 reason why I hate to reinstall Operation Systems, you lose so much tweaking that it's not funny...