postfix does not accept mail

[=?koi8-r?Q?=22?=Igor Shmukler=?koi8-r?Q?=22=20?=]

I have a problem with my Kolab setup.
Whenever I try to send mail from either remote or local machine to postfix I get error simmilar to 
following:
Original-recipient: rfc822;lamer at groupware.time.net
Final-recipient: rfc822;lamer at groupware.time.net
Action: failed
Status: 5.0.0 (Remote SMTP server has rejected address)
Remote-MTA: dns;groupware.time.net (TCP|167.206.5.xx|21833|68.79.248.xx|25)
 (groupware.time.net ESMTP Postfix)
Diagnostic-code: smtp;554 <lamer at groupware.time.net>: Recipient address
 rejected: Relay access denied

Could this have something to do with postfix LDAP cooperation? Is there a way to determine the 
cause?

Sincerely,
IS.