[Dovecot] Authenticate user thru PAM

[Adrian Mak]

my mailsystem is using postfix and virtual mailbox which stored in mysql db.
SMTP AUTH is using PAM, pam-mysql to authenticate against a mysql db.

I installed dovecot 0.99-14. In the dovecot example config file
it mentioned that auth_passdb can check against  thru PAM but auth_userdb didn't

Does it mean that auth_userdb should use other means e.g. /etc/passwd,
shadow, vpopmail, etc and in my case it is mysql. Right ?