problem with MX-record

[Stephan M. Ott // OKDesign oHG]

hi folks,
i recently set up a new domain for a customer on our server.
when checking out everything after succesful registration at the DENIC, i
received the following message from the system:

The original message was received at Sun, 27 Jun 1999 17:29:01 +0200
from xxx.okdesign.net [xxx.xxx.xxx.xxx]

   ----- The following addresses had permanent fatal errors -----
<info at xxx.de>
<webmaster at xxx.de>

   ----- Transcript of session follows -----
553 mail.xxx.de. config error: mail loops back to me (MX problem?)
553 mail.okdesign.net. config error: mail loops back to me (MX problem?)
554 <info at xxx.de>,<webmaster at xxx.de>... Local configuration error

(well, of course i substituted the domainname with xxx)

This is the entry in the DNS-File:

                        IN      NS      ns1.okdesign.net.
                        IN      NS      ns2.okdesign.net.
                        IN      MX      10 mail.xxx.de.
                        IN      MX      50 mail.okdesign.net.

xxx.de.                IN      A       xxx.xxx.69.19
mail.xxx.de.           IN      A       xxx.xxx.69.1
www.xxx.de.            IN      A       xxx.xxx.69.19

whereas the IP of mail.xxx.de is the main-IP of the server.

Last but no least I have the following entry in my /etc/mail/virtusertable:

@xxx.de                anyotheruser at anyotherserver

Any ideas what went wrong ?

Any help would be greatly appreciated.

Thank you in advance

-- Stephan