Tons of returned email from clients' newsletters

I have a client who has a rather large mailing list. They send a mailing out about once or twice a week. Whenever they do this about 300 returned emails are sent to nobody@servername.domain.com.

What do I need to do to make it so it will be returned back to their default account or their reply to address?

If I check this option under Tweak Settings in WHM "Prevent the user 'nobody' from sending out mail to remote addresses (php and cgi scripts generally run as nobody if you are not using phpsuexec and suexec respectively.)", will it fix the problem? I am currently running suexec but not phpexec. What difference would it make if I enable phpexec?

Any help would be greatly appreciated. I'm tired of having to go through and delete around 300 emails and make sure I'm not deleting any valid mail in the process!

cPanel.net Support Ticket Number:

 

They have an email address for the Reply-To field, but the from address was just a name and not an actual email address.

Thanks for your help!

cPanel.net Support Ticket Number: