distuguish between different domains

[Marco Fretz]

>> the dovecot service does not care about the server dns name. the dns
>> name resolves to the IP address on the client (roundcube) and the client
>> connects to the server. if the same dovecot instance listens to all /
>> both IP address, client will end up on this dovecot instance and all
>> valid user-password combinations are authorized. that's the way it has
>> to be, otherwise virtual / mass virtual domain hosting would not be
>> possible as you cannot spawn 1000 instances on the same machine (ok, in
>> theory you could do that :D)
> No, it's only impossible if you are using passdb or otherwise
> authenticating against real users of the system.  If you are using
> virtual users (SQL, LDAP, etc.), you can include the domain name in the
> auth lookups.
>
>
Andreas was asking about the fqdn where the imap client is connecting
to, not the user name / e-mail address.
you can use localpart and domain from the email address in passdb /
userdb lookups but dovecot (imap) is nothing like http where you send
the a hostname of the site you're conncting to in the header.