[Dovecot] Virtual Users, PAM authentication, MySql backend

Hi,

I'm sorry if this is a silly question, but i know that is not possible in Courier, so, I need to check if I can do it with Dovecot.

Can I use PAM authentication, witch get the users data from a external database (like mysql)? I've found many ways to do this stuff disconnectedly (like pam authentication with passwd ), but i can put all together? I can't use the passwd...

Thank's,

Álvaro