Question 1

What is MTA-STS?

Accepted Answer

MTA-STS (Mail Transfer Agent Strict Transport Security) prevents email from being intercepted in transit. It tells sending servers that they must use TLS encryption when delivering mail to your domain, and reject unencrypted connections. Without MTA-STS, a man-in-the-middle attacker can downgrade connections to plaintext.

Question 2

Why does MTA-STS matter?

Accepted Answer

Even though most email servers use TLS (encryption), without MTA-STS the encryption is opportunistic — an attacker can strip TLS from the connection and read emails in transit. MTA-STS makes TLS mandatory, not optional. Google, Microsoft, and other major providers support and recommend MTA-STS.

Question 3

Is this MTA-STS checker free?

Accepted Answer

Yes, completely free. We check the MTA-STS DNS record, fetch the policy file, and validate the configuration using public DNS queries and a simple HTTP fetch.

MTA-STS Checker