DNS & Email Trust
medium Severity
Free Check

MTA-STS Policy (Mail Strict Transport)

Validates RFC 8461 MTA Strict Transport Security policy to enforce TLS encryption for incoming SMTP mail delivery.

Test Your Website for MTA-STS Policy (Mail Strict Transport)

Run this check along with 90+ automated tests across your domain.

Why It Matters

Protects email exchanges from opportunistic TLS downgrade attacks and man-in-the-middle interception.

How We Check This

We check for a _mta-sts DNS TXT record and verify https://mta-sts.yourdomain.com/.well-known/mta-sts.txt exists.

How to Fix & Implement

Copy-paste configuration blocks tailored for your web server or edge proxy.

nginx snippet
# Serve policy file at https://mta-sts.yourdomain.com/.well-known/mta-sts.txt:
version: STSv1
mode: enforce
mx: mail.yourdomain.com
max_age: 604800

Frequently Asked Questions

What is the difference between MTA-STS and DANE?

MTA-STS relies on HTTPS PKI certificates, whereas DANE relies on DNSSEC.