I cannot seem to work this one out.

Client is using zoneedit for DNS because he is a reseller and does not want to use our DNS.

Now I cannot send mail to him. Nobody can. The error I get back when trying to send him mail is:

config error: mail loops back to me (MX problem?)
554 5.3.5 ... Local configuration error

As far as I know he can SEND mail just fine.

He has full dns/mx settings at zoneedit. He gave me his pw and I checked/corrected myself.
mail.hisdomain.com --->IP address
domainname -->mail is send to -->mail.hisdomain.com

Same setup on my server as well.

Somewhere I am going wrong thoug :confused:

Usually this problem occurs because Sendmail is not setup to accept mail for a particular domain. So, DNS may be setup correctly, but Sendmail probably has a misconfiguration.

Take a look at this:

http://www.redhat.com/support/resources/faqs/RH-sendmail-FAQ/x64.html

For more information.

is his domain listed in your 'local-host-names' file or simular file for your particular sendmail configuration?