duplicate messages sent

[Rich]

I have a client who uses Exchange for mainly a repository and also benefits
from public contacts and calendaring. The default email account in their
outlook client is a pop account and there is another account which is the
exchange account. The pop account is where they get their mail and send from
and the exchange account stores their mail on the server. I have been getting
reports that their mail goes out twice...it's a duplicate. I have looked at
the header and there is a reference from the pop mail as well as the exchange
server. I know it must be a setting/configuration on the exchange server. I
have a smtp connector on exchange. Is this necessary on exchange?
The following are the headers
1. This is from the header of the pop account.
Microsoft Mail Internet Headers Version 2.0
Received: from ylpvm01.prodigy.net ([207.115.57.32]) by velarium.com with
Microsoft SMTPSVC(6.0.3790.0);
Tue, 2 Nov 2004 15:49:12 -0800
2. This is from the header of the exchange account.
Microsoft Mail Internet Headers Version 2.0
Received: from sfgserver.sfgllc.local ([66.124.0.169]) by velarium.com with
Microsoft SMTPSVC(6.0.3790.0);
Tue, 2 Nov 2004 15:49:08 -0800

Any advice on this?
Thanks