Mailbox name diferent than login name in IMAP/POP, possible?

[Pedro Algarvio]

Is it possible to login like username at domain.tld and get the mailbox  
for that user to be for example username_domain.tld?

I'm using ldap as the saslauthd backend, so would it be possible to  
translate username at reaml to username_realm, that way users could login  
with their normal email address to services like pop/imap.

I know authentication is possible, that's plain ldap, but the mailbox  
"translation" is my doubt.

P.S.: I'd like to get this without using cyrus virtdomains setting, or  
at least leaving it to off.

Thanks!
-- 
Pedro Algarvio
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