Gmail making email more secure with MTA-STS standard

Posted by Nicolas Lidzborski, Senior Staff Software Engineer, Google Cloud and Nicolas Kardas, Senior Product Manager, Google Cloud 

We’re excited to announce that Gmail will become the first major email provider to follow the new SMTP MTA Strict Transport Security (MTA-STS) RFC 8461 and SMTP TLS Reporting RFC 8460 internet standards. Those new email security standards are the result of three years of collaboration within IETF, with contributions from Google and other large email providers.

SMTP alone is vulnerable to man-in-the-middle attacks

Like all mail providers, Gmail uses Simple Mail Transfer Protocol (SMTP) to send and receive mail messages. SMTP alone only provides best-effort security with opportunistic encryption, and many SMTP servers do not prevent certain types of malicious attacks intercepting email traffic in transit.

SMTP is therefore vulnerable to man-in-the-middle attacks. Man-in-the-middle is an attack where communication between two servers is intercepted and possibly changed without detection. Real attacks and prevention were highlighted in our research published in November 2015. MTA-STS will help prevent these types of attacks.

MTA-STS uses encryption and authentication to reduce vulnerabilities

A MTA-STS policy for your domain means that you request external mail servers sending messages to your domain to verify the SMTP connection is authenticated with a valid public certificate and encrypted with TLS 1.2 or higher. This can be combined with TLS reporting, that means your domain can request daily reports from external mail servers with information about the success or failure of emails sent to your domain according to MTA-STS policy.

Gmail is starting MTA-STS adherence. We hope others will follow

Gmail the first major provider to follow the new standard, initially launching in Beta on April 10th 2019. This means Gmail will honor MTA-STS and TLS reporting policies configured when sending emails to domains that have defined these policies. We hope many other email providers will soon adopt these new standards that make email communications more secure.

Email domain administrators should set up DNS records and web server endpoint to configure MTA-STS and TLS reporting policies for incoming emails. Use our Help Center to find out how to set up an MTA-STS policy with your DNS server. G Suite admins can use the G Suite Updates blog to see what MTA-STS means for G Suite domains.