a bit longer answer: smtpd is interfaced to bsdauth (see authenticate(3)). so if you want you can implement authentication method, just like I did to authenticate smtpd client to pop3 server.
authenticate(3) makes my head spin, it would be awesome if you shared how you did that! Has anybody else tried in general to interface with other virtual authentication databases, and wish to share some experiences?
Thnx! Kami