undelivered mail returned to sender

[jura]

HI !

I am a zimbra newbie, started using ZCS two weeks ago, evertyhing seem to be working just fine but now one of my clients keeps getting undelivered mail returned to sander notifications...


-------- Original Message --------
Subject: Undelivered Mail Returned to Sender
Date: Tue, 10 Feb 2009 16:56:59 +0100 (CET)
From: MAILER-DAEMON@albert.ifs.hr (Mail Delivery System)
To: mkralj@ifs.hr

This is the mail system at host albert.ifs.hr.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<Service@cern.ch>: host cernmxgwlb.cern.ch[137.138.142.186] said: 550 5.1.1
User unknown (in reply to RCPT TO command)


now i thought this could be a problem related to my dns mx settings so i check them and went to MX Lookup Tool - Check your DNS MX Records online run the diagnostics and everything turned out to be ok, but my clients mail to one specific e mail address keep bouncing any ideas ?


Thank you in advance....

[uxbod]

So is the bounced email from your server or a remote one ? ie. is this inbound or outbound email.

[jura]

albert.ifs.hr is my mail server...email is outbound