As a systems administrator dealing with Yahoo Mail can be a pain. For the sysadmin of a system that sends promotional, opt-out mailings it can be brutal. I'm still trying to figure out why I can never actually talk to a human over there.

To put it another way, Yahoo's spam algorithm is so poor that they blindly tag items as SPAM if they contain so much as a one promotional message or if a user flags it as SPAM out of anger. Contrast this behavior to that of Microsoft's Live Mail or Google's Gmail and you'll begin to see the difference. On most occasions the messages make it through Live Mail or Gmail but somehow end up in the Yahoo Mail spam folder. I've read similar complaints from other sysadmins.