[Exim] EXIM issues...

Can anyone help me? I've just taken over administration of a Debian Linux
box that's running Exim mail which, from what I understand, is a derivitive
of Smail. As the postmaster I continually get these "frozen" messages.
Here is an example of one of the thousands of messages the postmaster
receives daily:

Message 14Rng8-00007P-00 has been frozen. The sender is
<eai@???>.

The following address(es) have yet to be delivered:
eai@???: remote host address is the local host

Does anyone know what this means and how I can rectify it. If anybody has
any ideas I would really appreciate it.

Thanks in advance!