auth_username_translation seems to be appliet on RCPT TO address of LTMP 
transport.
Why dovecot is doing that? 
And better question - is there a way to disable auth_username_translation for 
LTMP but leave enabled for the rest (imap, pop3 etc) ?
Background:
I'm doing
auth_username_translation = @
to allow logins like aaa at bbb.pl to be internally translated to aaa=bbb.pl. 
That works fine.
Now my exim delivers mail to dovecot using LTMP and it does translation or it 
own, so it does:
RCPT TO: <aaa=bbb.pl at mymbox.pl>
Unfortunately looks like dovecot it doing translation one more time and 
looking in user database for aaa=bbb.pl=mymbox.pl where such user doesn't 
exist. Only aaa=bbb.pl user exists.
Thanks,
-- 
Arkadiusz Mi?kiewicz, arekm / maven.pl