Have you tried checking with your ISP to see if they are blocking SMTP ports on your system? I know that my ISP does block me from sending mail using my work server via port 25. The server for my work account is specifically set to a different port to get around this problem. Might be what's happening to you.
A lot of ISP's have done this to try to cut down on zombie spam being sent through their servers apparently.
HTH!
Useless trivia: In the 2004 Las Vegas phone book there are approximately 28 pages of ads for massage, but almost 200 for lawyers.