what is sending out emails

I am running Postfix, and Nagios on the same server.
Postfix is set to use my exchange server as a relay, works just fine.
People get the emails that Nagios sends out just fine an dandy.

Now for the problem.

Randomly, an email gets sent out (seemingly from Nagios) but the "to" address is "$@<mycompanydomain>.com obvioulsy it gets rejected. and I only found out about it as I created an exchange mailbox for the return address I setup in postfix.

None of the logs in Nagios show that it sent the email.

Anyway to find out how and where postfix was given a message to send??

Here is an example of the maillog:
Aug 12 16:43:25 g1vpnag01 postfix/smtp[896]: 1C56713F9D2: to=<[email protected]>, orig_to=<$>, relay=10.100.9.19[10.100.9.19]:25, delay=0.61, delays=0.02/0/0/0.59, dsn=2.6.0, status=sent (250 2.6.0 <[email protected]> [InternalId=6329805] Queued mail for delivery)
Aug 12 16:43:25 g1vpnag01 postfix/qmgr[24520]: 1C56713F9D2: removed

 

Have you configured Exchange to accept the Messages from your Nagios server, check link

 

Yes, as i mentioned, valid emails from nagios are sent and delivered just fine.