Mailing list software recommendation?

I'm looking for PHP/MySQL based mailing list software for a project I'm doing.. I plan on hosting a bunch of virtual domains and having to set up mailing lists for all of them, and I don't want to go installing a new copy of the software for each virtual domain. The rest of the site is in PHP and uses a MySQL back-end for user-authentication and authentication to other software (tying in a bulletin board/forum login, and some other custom things), so I definetly want MySQL involved for the authentication. Any suggestions? I've been poking around for a little while and I haven't really seen anything addressing the virtual domain issue.. I'm sure there's something out there, ISPs and such have to be using something, I just don't know what it is.. Thanks, Chad