Well, this is completely f'd up. Suddenly, outbound SMTP mail from Evolution on my Fedora 10 install just stopped working. The only thing I had done was install Alpine, the most recent version of what used to be the Pine command line email program.
Digging further, I found this post suggesting that both Compuserve and Comcast have been using port 587 instead of port 25 to receive SMTP email.
Thanks Comcast. You just killed more than two hours of my time. You incompetent fools.