the emailgtw probe is looking for a message with a subject of email.
There would have to be a script or an AO profile that is posting a message with a subject for the emailgtw to pickup.
you can edit the nas.cfg and search for email and see what that probes.
You can also set the nas debug level to 3 or higher and you should be able to see the profile firing for this.
You may need to check your scripts as well.
hope this helps