[Dovecot] imap and vpopmail: per-domain auth

[Francesco Abeni]

Hi, i have qmail + vpopmail + dovecot + squirrelmail 0.99.14 on Fedora 
Core 4. Qmail includes its own pop3 server, and everybody is able to 
access it from outside. Dovecot is used only locally by SquirrelMail - 
so everybody can access via webmail.

I'd like to make imap directly available from outside, but only for a 
few selected domains (NOT ip addresses!), while leaving everyone able to 
access with pop3 and/or via webmail.

I don't know if this is possible, and if it is, i don't even know where 
to start. Is it a vpopmail or dovecot setting?

Thank you for any suggestion and/or pointer to the right documentation.

-- 
Francesco