What is the primary purpose of MTA-STS reports?

The primary purpose of MTA-STS reports (specifically TLS-RPT reports) is to provide domain owners with feedback on the TLS encryption status of inbound email connections. They help verify that email sent to your domain is always delivered securely and flag any failures or issues.

Why might I receive these reports from Google but not other providers?

You might receive these reports from Google more than other providers because Google (Gmail) was one of the earliest and most active implementers of MTA-STS and TLS-RPT. Their widespread adoption ensures that if your domain supports these standards, Google will actively participate in sending reports.

How often should I expect to receive MTA-STS reports?

TLS-RPT reports are typically sent daily, but the frequency can vary depending on the sending mail server and the volume of email traffic to your domain. You might receive them less often if your domain receives little email from supporting senders.

What should I do if my MTA-STS reports show failures?

If your MTA-STS reports show failures, you should investigate the failure-details section of the report. Common issues include expired TLS certificates, misconfigured MX records, or errors in your mta-sts.txt policy file. Resolve these issues to ensure secure email delivery.

Is MTA-STS required for email deliverability?

MTA-STS is not strictly required for email deliverability, but it is highly recommended. It adds an essential layer of security by enforcing TLS encryption for inbound mail, helping to prevent man-in-the-middle attacks and ensuring the privacy of your communications. Along with SPF, DKIM, and DMARC , it contributes significantly to your domain's overall email security and sender reputation.

What are MTA-STS reports and why am I getting them from Google? - Technical - Email deliverability - Knowledge base

Receiving email reports, especially from a major provider like

Google, detailing Mail Transfer Agent Strict Transport Security (MTA-STS) activity might seem a bit unexpected at first. These aren't just ordinary notifications, they are crucial indicators of your domain's email security posture and compliance with modern standards.

The arrival of these reports signals that your domain has likely implemented MTA-STS, a security mechanism designed to enforce Transport Layer Security (TLS) encryption for inbound email. When you receive these, it means external mail servers (like Google's) are actively checking your policy and reporting on their attempts to deliver email securely to your servers.

This process involves not just MTA-STS itself, but also its companion, TLS Reporting (TLS-RPT). Together, they provide invaluable insights into how well your email infrastructure is protecting messages in transit, especially against potential man-in-the-middle attacks and downgrade attacks.

What are MTA-STS and TLS-RPT?

MTA-STS, defined in RFC 8461, is an email security standard that allows a domain to declare that its Mail Transfer Agents (MTAs) expect to receive emails over connections secured with Transport Layer Security (TLS). Essentially, it's a way for your domain to tell sending mail servers, "Always encrypt emails sent to me, and validate my certificate."

Without MTA-STS, if a secure TLS connection fails, the sending server might downgrade to an unencrypted connection, making your email susceptible to eavesdropping. MTA-STS prevents this downgrade by instructing the sending server to either enforce TLS or drop the connection if it cannot establish a secure one that meets the policy requirements. This significantly enhances the privacy and integrity of your inbound email traffic.

Complementing MTA-STS is TLS Reporting (TLS-RPT), outlined in RFC 8460. This protocol enables you to receive aggregated reports from sending mail servers about their attempts to deliver email to your domain using TLS. These reports, often sent daily, provide visibility into successful connections and, more importantly, highlight any failures or issues related to TLS negotiation, certificate validation, or MTA-STS policy adherence. It's similar to how DMARC reports provide insights into email authentication.

Why Google sends these reports

You are likely receiving these reports from Google because your domain has published both an MTA-STS policy and a TLS-RPT record in your DNS. Google was an early adopter and strong advocate of these standards, making it one of the primary senders of these security reports.

When Google (or any other supporting mail server) attempts to deliver an email to your domain, it first checks for an MTA-STS policy. If found, it will try to establish a TLS-encrypted connection strictly following your declared policy. The outcomes of these attempts, whether successful or not, are then compiled into a report and sent to the email address specified in your TLS-RPT DNS record.

So, getting these reports isn't a problem, it's actually a sign that your email security measures are being acknowledged and that you're receiving valuable feedback. It means Google is helping you monitor and maintain the security of your inbound email communications.

These reports are usually sent from an address like noreply-smtp-tls-reporting@google.com, confirming their origin.

Sample TLS-RPT DNS record

DNS TXT record for TLS ReportingDNS

_smtp._tls.yourdomain.com IN TXT "v=TLSRPTv1; ru=mailto:reports@yourdomain.com"

This DNS record tells sending servers where to send the TLS reports. The ru tag specifies the reporting URI, which is typically an email address.

Understanding the reports

TLS-RPT reports are typically sent in JSON format and contain a wealth of information. They detail the overall number of connections, how many succeeded with TLS enforcement, and how many failed. For failures, they often provide granular details about the nature of the problem, such as certificate errors, expired certificates, or policy mismatches. Analyzing these reports is key to diagnosing and fixing email deliverability issues.

I often see Google Postmaster Tools users check their DMARC reports, but these TLS reports are equally important for a holistic view of email security and deliverability. They help identify underlying network or certificate issues that could prevent emails from reaching their destination securely. This is especially important for companies that must meet compliance requirements regarding data privacy.

By actively monitoring these reports, you can quickly spot and resolve configuration errors. This proactive approach ensures that your domain's MTA-STS policy is working as intended, securing your inbound email traffic and maintaining sender reputation.

Field	Description
organization-name	The name of the reporting organization (e.g., Google).
date-range	The period for which the report data applies.
contact-info	Contact details for the reporting entity.
policy-domain	Your domain for which the policy applies.
policy-type	Indicates the type of policy, typically mta-sts.
total-successful-session-count	Total TLS connections that succeeded.
total-failure-session-count	Total TLS connections that failed.
failure-details	Specific reasons for connection failures.

Common issues in reports

Certificate validation errors: Indicates issues with your TLS certificate, such as being expired, revoked, or not trusted.
Policy mismatches: The policy discovered via DNS doesn't match the one on your web server.
Downgrade attacks: If an attacker attempts to force an unencrypted connection.
DNS configuration problems: Incorrect or missing MTA-STS or TLS-RPT DNS records.

Potential solutions

Update certificates: Ensure your TLS certificates are current and valid.
Verify policy file and DNS: Double-check that your mta-sts.txt policy file matches your DNS record and is accessible.
Review MTA configuration: Ensure your mail server is correctly configured to enforce TLS 1.2 or higher.
Consult Google resources: Use tools and guides provided by Google to troubleshoot specific errors.

Implementing MTA-STS and TLS-RPT

Implementing MTA-STS and TLS-RPT for your domain involves a few key steps. First, you need to create an MTA-STS policy file, usually named mta-sts.txt, and host it on your web server at a specific path: https://mta-sts.yourdomain.com/.well-known/mta-sts.txt. This file specifies the required TLS versions and acceptable MX (Mail Exchange) records for your domain.

Next, you need to publish a DNS TXT record for MTA-STS policy discovery. This record, typically _mta-sts.yourdomain.com, signals to sending mail servers that your domain has an MTA-STS policy and where to find it. The id tag in this record should be updated whenever you change your policy file to prompt sending servers to refresh their cached policies.

Finally, you set up the TLS-RPT DNS TXT record (_smtp._tls.yourdomain.com) pointing to an email address where you wish to receive the compliance reports. This record is critical for getting the feedback needed to monitor and troubleshoot your MTA-STS implementation. Setting up these records correctly is vital for optimal email deliverability.

Best practices for implementation

Gradual deployment: Start with a testing or enforce policy mode, similar to DMARC policy rollout, to avoid disruption.
Consistent updates: Update your MTA-STS policy id whenever there are changes to your MX records or certificate setup.
Monitor TLS-RPT reports: Regularly review incoming reports to identify and address any issues promptly, similar to DMARC report analysis.
Secure your web server: Ensure the web server hosting your mta-sts.txt file is properly secured with HTTPS.

Views from the trenches

Best practices

Always keep your MTA-STS policy file and DNS records synchronized.

Regularly check TLS-RPT reports for any anomalies or failures, even if minimal.

Consider a phased deployment starting with 'testing' mode before moving to 'enforce'.

Common pitfalls

Forgetting to update the 'id' tag in the MTA-STS DNS record after policy changes.

Misconfigurations in the mta-sts.txt file, leading to policy parsing errors.

Not having a valid, trusted TLS certificate for your MX hosts.

Expert tips

Set up alerts for significant increases in TLS-RPT failure rates to detect potential attacks or misconfigurations.

Leverage automated tools to monitor MTA-STS policy and report on TLS compliance.

Ensure all your inbound mail servers (MX records) support the TLS versions and certificates defined in your MTA-STS policy.

Marketer view

Marketer from Email Geeks says they started receiving MTA-STS reports from Google recently, noting that before that, only Comcast sent occasional reports.

September 25, 2023 - Email Geeks

Marketer view

Marketer from Email Geeks says they get daily reports for their personal domain ever since configuring MTA-STS.

September 25, 2023 - Email Geeks

Embrace the reports

Receiving MTA-STS reports, particularly from Google, is a positive sign for your email security efforts. It indicates that your domain is participating in a crucial standard that helps enforce TLS encryption for inbound emails, protecting them from various attacks.

These TLS-RPT reports are not just confirmations of compliance, but also vital diagnostic tools. By regularly reviewing them, you gain invaluable visibility into potential issues with your mail server's TLS configuration, certificate validity, or even network connectivity. Promptly addressing any reported failures ensures that your email remains secure and reaches its intended destination without compromise.

Embracing and actively managing MTA-STS and TLS-RPT positions your domain at the forefront of email security, contributing to a more trusted and resilient email ecosystem overall.