Mailserver cannot recive E-Mail's

[ChRiStHeTuNeR1993]

Hello together!

First sorry for my bad Language! Im german and my english is not the best :S

So:

I have a Virtual Server with OpenSUSE 11.4 and Plesk 10.3.1 on it.

I wanna use the cool Mailserver on one of my Domain's!

wehn i add a E-Mail adress i can Send mails!

but i cannot recive a reply!


I bekome the e-mail back with this:

This is the mail system at host fmmailgate02.web.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 mail system

<spam@d42c-clan.eu>: host mail.d42c-clan.eu[89.202.0.34] said: 550 unknown user
(in reply to RCPT TO command)

What t do?

Please help me!

greetings Chris!