Definition
Without it, mail can downgrade to plaintext on transport. The policy tells senders to forbid insecure delivery.
Best Practices
- Publish the MTA-STS policy file over HTTPS.
- Start in testing mode with a valid TLS report address.
- Monitor reports and upgrade to enforce gradually.
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Frequently Asked Questions
A standard to require TLS for receiving mail connections.
A JSON policy served over HTTPS that receivers fetch.
Senders refuse insecure transport to the domain.