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.
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.