If you ever send mail from any sites that's on the same server where your site
is hosted your external mail server will not receive the mail. The reason for this is
that a server will always try to send locally before it tries what the actual DNS
zone points to. The way to fix this is to open a ticket here (hosting support)
and in the body of the
"Please remove my domain ****.com from /etc/localdomains and
add it to /etc/remotedomains".
Only we are able to make this change for you. After the change is completed,
this problem should be fixed.