A long time ago I built a Nagios script for verifying email end to end. It would trigger a test email to be sent from the app to a known mailbox and measure the time to receipt in that mailbox. Simple but extremely effective, and several times it caught a failing in the mail stack somewhere.
It also got used to validate enquires@/hello@/contact forms were delivering, especially to set small business owners minds at rest.
It also got used to validate enquires@/hello@/contact forms were delivering, especially to set small business owners minds at rest.