TLS Transport Security

MTA-STS & TLS 1.3 Transport Security Impact Calculator

Model man-in-the-middle (MITM) downgrade attack prevention and Google SMTP TLS compliance scoring.

Monthly Inbound/Outbound Mail Volume 2,000,000

MTA-STS Policy Mode enforce (Strict Mandatory TLS)

TLS-RPT (TLSRPT Reporting) Enabled (Daily Telemetry)

Transport Encryption Level

100% TLS 1.3

Zero plaintext downgrade permitted

MITM Downgrade Protection

IMMUNE

STARTTLS stripping defeated

Max-Age Policy TTL

604,800 sec

7-day receiving cache

Google / Gmail Trust Score

MAXIMUM

Gold standard for bulk senders

MTA-STS Policy File (mta-sts.txt)

version: STSv1 mode: enforce mx: mail.yourdomain.com max_age: 604800

Deploy Automated MTA-STS & TLS-RPT with AutoSMTP

AutoSMTP provisions HTTPS policy endpoints and automated SSL renewals.

Deploy Dedicated MTA →

The Necessity of MTA-STS (RFC 8461) in Modern Email

Standard SMTP encryption relies on opportunistic TLS via the STARTTLS verb. An active attacker on the network can strip the STARTTLS command, forcing the email to transmit in cleartext without either party being alerted.

STARTTLS Downgrade Prevention

MTA-STS publishes an HTTPS policy file telling all sending MTAs that your domain requires TLS. If TLS cannot be negotiated with a valid certificate, the connection is refused.

TLS-RPT Daily Reporting

With TLS-RPT configured, senders like Google and Microsoft transmit daily JSON failure reports notifying you if certificate expirations or network tampering occurred.

Enterprise Compliance

Mandatory MTA-STS adoption satisfies HIPAA, SOC 2, and GDPR requirements for non-repudiable encryption of data in transit across public networks.