MTA-STS Validator

Secure Your Domain's Inbound Email Traffic

Ensure your domain's inbound email traffic is secure with our MTA-STS (Mail Transfer Agent Strict Transport Security) Validator. This tool checks your MTA-STS policy for proper configuration, validates syntax and DNS records. Protect your organization from man-in-the-middle attacks and unauthorized interception by enforcing a reliable and secure MTA-STS setup.

What is MTA-STS?

MTA-STS (Mail Transfer Agent Strict Transport Security) is a policy that lets supporting sending servers acknowledge that encrypted delivery to your domain is possible. It instructs these servers to avoid delivering emails if a secure TLS connection cannot be established. However, sending servers that do not support MTA-STS can still send emails over an unencrypted connection, meaning MTA-STS does not enforce encryption universally.

Why is MTA-STS Important?

Signal TLS Support for Inbound Emails: Allows sending servers to verify encrypted delivery is possible to your domain.
Prevent Downgrade Attacks: Encourages encrypted delivery by blocking servers claiming encryption is unavailable.
Protect Against Man-in-the-Middle Attacks: Reduces the risk of message interception or tampering for supporting servers.
Enhance Organizational Security: Demonstrates a proactive approach to secure communications.

How Does MTA-STS Work?

Policy Publication: Publish an MTA-STS TXT record in DNS and host a policy file over HTTPS.
Policy Verification by Senders: Sending servers that support MTA-STS check your policy to determine if encryption is possible.
Encourage Secure Delivery: Messages are only delivered via secure TLS connections. Otherwise, they are not delivered.

Common MTA-STS Issues

Incorrect DNS Configuration: Missing or improperly formatted TXT records.
Policy File Errors: Incorrectly formatted `mta-sts.txt` files.
Certificate Problems: Expired or mismatched certificates can prevent proper encryption.
Transition Issues: Moving to "enforce" mode without testing can disrupt email delivery.

Best Practices for MTA-STS

Start with "testing" mode to validate your setup before moving to "enforce" mode.
Host your policy file over HTTPS and ensure it is accessible.
Keep TLS certificates valid and trusted to support encrypted delivery.
Monitor email traffic and logs during testing to identify potential issues.
Maintain accurate and consistent DNS records for MTA-STS.

New to MTA-STS?

Check out our blog to learn what it is and how it secures your inbound email.

Read the blog

MTA-STS survey

Discover the latest insights on MTA-STS adoption in our 2024 survey

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