Separate names with a comma.
Have you tried going into WHM, under the Exim Configuration disable the setting "Verify the existence of email senders".
I have found simply forwarding the IP via named works fine, haven't had a problem with that at all.
Have you tried building with 4.3.10, but not using your old configuration settings, but choosing your options again?
I would suggest downloading and installing RootKit Hunter and running it on the server to be sure that there is nothing wrong. After you install...
You should really get a professional too look at the server and diagnose it, you may have to have the server restored, there is alot of server...