mail for xyz.de loops back to myself?

[Dominik Elsbroek]

Hi there,

I have the following error occurring if a send a mail to an e-mail
address at my domain:
All mails send to my kolab server return with message body:

This is the Postfix program at host www.xyz.de.

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 Postfix program

<technik at xyz.de>: mail for xyz.de loops back to myself

whats the problem? i installed kolab with hostname www.xyz.de and as
mailserver i entered xyz.de. Do I have to enter both times only xyz.de
or is my configuration at another point wrong?
any hints?

regards 
Dominik Elsbroek