Different realm for different listeners?

I see this has been asked a few times over the years (but not in several years), and the response was along the lines of "maybe someday", so I figured I'd see if someday was here yet...

I have a need to have a different default realm for different listeners. Basically, I've a bunch of different domains, and a few of them insist their users not be required to authenticate with "user@domain" and just use "user", and I'm trying to make this work without separate daemons and/or VMs.

I'll be using Dovecot 2.2 (most likely 2.2.10 as provided by RHEL/CentOS 7).

Thanks. If there's not a way to do this directly in Dovecot, does anybody have any suggestion that doesn't require several different VMs?

Chris Adams cma@cmadams.net