Question : email bounce back

hello i have issue with email bounce back,

i have sendmail server with hostname : s1.moon.com

so let say i sent email to [email protected], then my datacenter dns cannot resolved it and emaul bounce backed. but bounce backed error will show the email recipient with moon.com at behind the domain. the error like bellow :

All attachments
----- The following addresses had permanent fatal errors -----

   (reason: 553 5.3.5 system config error)

  ----- Transcript of session follows -----
553 5.3.5 omegaone.com.moon.com. config error: mail loops back to me (MX problem?)
554 5.3.5 Local configuration error


my question is why moon.com appear at behind valid email address ?
where is the conf file i have to fixed the problem ?
any suggestion how to solved ?

sorry for so much question, domain above just for example only and not exist.

Answer : email bounce back

Ask webvis.net to remove that dns entry and let's start again.