Authentication and maibox name

[Roman Golub]

Hi all,

cyrus-imapd-2.3.11
cyrus-sasl-saslauthd-2.1.22
Authentication: saslauthd -> PAM -> RADIUS

imapd.conf:
...
virtdomains: no
loginrealms: domain
...

There is a mailbox mbox001 (/var/spool/imap/user/mbox001)
For access to this box the user is authenicates with a name mbox001

Now it is necessary that the user could access into that mailbox both
under a name mbox001 and under a name mbox001 at doman 
Authentication for names mbox001 and mbox001 at domain passes successfully
as in both cases to RADIUS passes query for user mbox001,
but Cyrus gives out an error "Invalid mailbox name" for mbox001 at domain

What is mailbox Cyrus searches for in this case?
Is there something that can do to specify Cyrus that
when user mbox001 at domain is authenticated it needs to use a box mbox001?

Thanks.