[Dovecot] Virtual Servers, or different authentication setups.

I want to know if there is any virtual server functionality in Dovecot?

I would like to have two separate configurations, that access the same email, running in the same Dovecot instance. They would bind different ports and/or IPs, but have different authentication settings. In particular, one would use a PLAIN password scheme, the other SSHA.

How would I go about setting up these virtual servers? Or, would I have to run separate instances of Dovecot? If I do have to run separate instances, how do I keep them from interfering with eachother?

-Josh