[Dovecot] proxy, userdb and passdb

Dear all,

We are getting closer to the migration of our mailsystem. Now I have a special question. We are successfully using

passdb { driver = pam }

and that is good. Now, how would I tell dovecot to proxy certain users (the ones not yet migrated) to the old server? My attempts to configure an additional userdb failed since this seems to override the passdb setting.

Grateful for any hints!

Cheers,

j.hofmüller

Optimism doesn't alter the laws of physics. - Subcommander T'Pol