So, yeah. I'm very happy. The whole setup and everything was made very easy by this guide: http://en.gentoo-wiki.com/wiki/Mail_ser ... nd_Dovecot
And now I have a working email system for the family Web site. I also found out how to relay my outgoing mail via my ISP's server. (Which I had to do because GMail wouldn't accept mail from my server.) I don't anticipate a high volume, so I don't think my ISP will mind too terribly. (Especially since I have to provide a username and password.)