DELIVTERMS: MTA-STS

It's time for another installment of our DELIVTERMS series here on Spam Resource, where we help you digest and understand the alphabet soup of email technology. Today, we're looking at MTA-STS (and TLS Reporting).MTA-STS stands for: Mail Transfer Agent-Strict Transport Security.The concept behind MTA-STS is actually pretty straightforward. It's essentially a way for an email receiver to tell the rest of the internet: "I only speak encrypted. If you can't guarantee a secure connection, don't even bother trying to deliver the mail."The Problem: SMTP Encryption Isn't MandatoryTo understand why we need MTA-STS, we have to look at how email encryption usually works. For a very long time,, we've relied on something called STARTTLS. When one mail server (the MTA) connects to another, it basically asks, "Hey, do you support encryption?" If the receiving server says yes, they wrap the conversation in a secure TLS (Transport Layer Security) tunnel.The problem? STARTTLS is opportunistic, meaning…