The problem with SMTP is that it is too simple. There is a complete lack of security, so different implementations have had layers added on top to harden them, which adds to the complexity. Not all layers are standardised or compatible, which means that what should be relatively simple becomes an untenable mess.

It isn’t something that can be proprietarised easily so companies need to also add their own proprietary layers in order to monetise their product, which adds more untenable.

If your “senior network engineer” is more concerned about your SMTP server becoming a SPAM relay than your product being usable for its intended purpose, which is why it is still down.