E-Mail Issue

[u-hosts]

MY hosting clients are moaning about this:

1. When ever they send an e-mail from their domain it goes in this format:
<usernam>@<hostname of the server> on behalf of; <E-Mail address Owner's Name [info@e-mailaddress.com]

Their domain name (suppose) it is e-mailaddress.com and my server's hostname is server.xyz.com and username is ABC and E-Mail address belongs to ABC the mail format is:

ABC@server.xyz.com on behalf of ABC [info@e-e-mailaddress.com]

So, my clients doesn't want to see server.xyz.com when they send out e-mails.

Is there anything I should do to get rid of those lines?

Thanks in advance.

[webignition]

http://forums.cpanel.net/showthread.php?t=53333

[u-hosts]

Thanks a lot