DadaMail (nee MojoMail) has been a great piece of software for handling multiple company mailing lists. I used it to send 5,000 messages at a time while at Virtual Access Networks, but I'm just not into perl anymore so I've started to look into PHP-based list software. I just installed phplist, and that was a relatively good experience. I haven't had a chance to really write it up yet, so I'm curious if anyone else has stories to share about mailing list managers.
Actually, I'm not convinced that anyone wants to be on a mailing list anymore. The only lists that I'm a member of are true list-servs. Otherwise, I can get updates via blogs and RSS on a daily basis.