I have seen code out there to use PHP to send an email to an SMTP server but it does not mean that the email went out properly.
I am wondering if you all have come across and end to end test of an SMTP server which would:
Send a test email from SMTP to another server
Retreive that email
presumably there would be an ID in the email so that if this was done on a regular basis, the sent email could be connected to the received email.
Obviously this really would be testing the uptime of two servers and the inet connection between the two unless the SMTP server sent an email to itself.