[Dovecot] Allowing non-SSL connections only for certain Password Databases

[Dan Pollock]

I'm trying to set up my system (using Dovecot 2.0.9) so that certain Password 
Databases are available over pop3 and imap and others are available over pop3s 
and imaps.

In particular, I would like users to be able to connect without SSL to accounts 
set up in vpopmail, but to require SSL for system accounts. 

Is there a way to set "disable_plaintext_auth" to different values for 
different Password Databases? Is there another way to do it? 

Thank you,
        Dan