Exchange 2003.
There's your problem.
I tried it as well, could not get it to work.
But now it is working as we're running on Exchange 2010.
By the by, you should be able to get it to work with port 80, but do remember that by using port 80, you are sending usernames and passwords via cleartext, which makes it easy for ne'er-do-wells to sniff your usernames/passwords and start spamming, or hacking your server.