[Dovecot] Error: auth(default): Unknown userdb type 'mysql'

Hi there, I have configured dovecot with mysql but when I restart (Redhat enterprise 4) the following error appears:

dovecot: Nov 01 18:47:08 Info: Dovecot v1.0-stable starting up dovecot: Nov 01 18:47:09 Error: Auth process died too early - shutting down dovecot: Nov 01 18:47:09 Error: auth(default): Unknown userdb type 'mysql' dovecot: Nov 01 18:47:09 Error: child 30738 (auth) returned error 89

I have all RPMs for mysql installed, as well as mysql-devel.

how can I verify that mysql support was correctly compiled in? sugestions?

Thanks in advance.