one day my ox server stopped receiving mail, it can send but not receive i put the command mailq and gives this

(Host or domain name not found. Name service error for name=com.com type=A: Host not found, try again)
testuser@com.com

5568E4F051E 7487 Tue Mar 25 15:17:01 root@com.com
(mail transport unavailable)
root@com.com
my host is something like testuser@example.com and it is resolving to testuser@com.com

??????????????
somebody know about this and how to resolve?