Is there a way of configuring a nagios check that a smtp service is correctly configured and emails are going out.

I have a check that the service is running, but recently we noticed that the configuration had been altered and no emails where going out, but the service was still running.

One idea I had was to schedule a regular email to be sent, is it possible for nagios to check for that email and throw an alert if it didn't detect it?

Any other ideas to monitor this gratefully received.