Recently we have started to see several Email messages from locally hosted Email accounts being delivered or responded to Mailer-Daemon@host.domain.com (our cPanel server).

This recently started to happen and appears that most (99%) of the messages are automated out-of-office replies.

What we can't figure out is why their mail clients are replying to "mailer-daemon" instead of who sent the message in the first place.

The option in the Exim configuration to not allow Email to the host name doesn't apply apparently when the messages are coming from local mail accounts.

Since the message header has no other information, we don't know where else to turn to help troubleshoot or prevent this from happening.

Any help is appreciated.