Email server for Linux

[Lorenzo Prince]

Hi.
Can anyone recommend a good mail server for Linux that supports multiple domains and has a web interface with a signup or new user page?  I am currently running such a server on my windows system, but I want to transfer all my servers to use Linux instead, because the more I use Linux, the more I love it.  But this is the only thing right now that is keeping me from keeping my dual-boot windows/Linux system booted into Linux at all times.  I would appreciate any and all help and/or recommendations in this matter.
Thanks,
Lorenzo Prince
lorenzo at princenet.sytes.net