MTA-STS Checker

Check if your MTA-STS (SMTP MTA Strict Transport Security) policy is configured correctly

About MTA-STS

MTA-STS (SMTP MTA Strict Transport Security) is a security standard that enables mail service providers to declare their ability to receive Transport Layer Security (TLS) secure SMTP connections, and to specify whether sending SMTP servers should refuse to deliver to MX hosts that do not offer TLS with a trusted server certificate.

How MTA-STS Works

  1. Sending mail server checks for MTA-STS DNS record at _mta-sts.yourdomain.com
  2. If record exists, fetches policy file from https://mta-sts.yourdomain.com/.well-known/mta-sts.txt
  3. Policy specifies which MX hosts support TLS and the enforcement mode
  4. Sending server enforces TLS when delivering email based on policy

Policy Modes

testing
Monitor mode - emails are delivered but failures are reported
enforce
Strict mode - emails must use TLS or delivery fails
none
Disabled - MTA-STS is not active
Recommendation: Start with mode "testing" to monitor compatibility, then move to "enforce" for maximum security.

Related Tools

MTA-STS Generator TLS-RPT Check TLS-RPT Generator DMARC Lookup Domain Check

Monitor MTA-STS Policy Health

Get real-time monitoring of your MTA-STS policy and TLS-RPT configuration. Receive alerts for policy issues and delivery failures.

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