Confirm an email was delivered

Is it possible for nagios to confirm that an email was received by an Exchange server? We have had cases in the past where everything seemed to be OK with an Exchange server, but email was still not going through.

Everything that nagios checks was up. SMTP service, all Exchange services, port 25 connections, disk space, etc. Email might have been blocked by a DNS problem, queue problems etc.

My thought is if I can have nagios check that an email was received, it confirms that Exchange was working as expected.

Any ideas are greatly appreciated.

Cesar Diaz