On a Win2k machine, there's no better recommendation than MDaemon. I've been running my own "hotmail" type service for about 2 years now on MDaemon. It's a full-featured mail server and built-in webmail client. They started out slow as far as features, but as of now, version 5.0, I can't think of a single feature they've left out. I'm sure there are many equally comparable for Linux, but there's nothing out there better than MDaemon for Windows. God, I sound like a commercial! I don't mean to, but MDaemon is hands-down the best piece of software I've ever seen. =)