problem to receive email

Hello,

I've got a probleme with mail on my server. The server can send them. But can't receive them. And i dont find why. Here is the error mail that i receive when i try to send me an email on contact@myrealdomain.fr

from : Mail Delivery System <MAILER-DAEMON@localdomain>

This is the mail system at host sd-29xxx.localdomain.

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

<contact.myrealdomain@localdomain> (expanded from contact@myrealdomain.fr): Host or domain name not found. Name service error for name=localdomain type=A: Host not found

Final-Recipient: rfc822; contact.myrealdomain@localdomain Original-Recipient: rfc822;contact@myrealdomain.fr Action: failed Status: 5.4.4 Diagnostic-Code: X-Postfix; Host or domain name not found. Name service error for name=localdomain type=A: Host not found.

Thanks for help