On 11.5.2011, at 18.49, Oliver Eales wrote:

is it possible to have dovecot imap listening on two different ports, while providing different auth_mechamisms and different pass_db/user_dbs ?

Not currently.

Or is it better to simply have two running dovecot instances on the same machine ?

For now, yes. In future you could put auth settings inside local {} blocks. Although even that only supports different IPs, not ports. But maybe ports could be added also some day..