TLS-RPT delivers daily reports about TLS failures on your inbound email — helping you debug MTA-STS and DANE issues. TLS-RPT sits in the part of the mail flow where identity, sender reputation, and enforcement meet. The details matter because one weak link can undo the work done by the other controls.
If you are already working through MTA-STS and DANE, this topic gives you the missing layer between the raw signal and the decision you have to make. For a live check, start with the CyberFurl TLS-RPT check and then use the See the email authentication feature page to see where it fits in the wider CyberFurl workflow.
What's in a TLS-RPT report
A TLS-RPT report summarizes transport failures that senders encountered when trying to deliver mail with expected TLS protections. Depending on the reporter, it can show counts, failure reasons, affected MX hosts, and whether problems were tied to MTA-STS or DANE expectations.
That makes it useful less as a daily inbox item and more as an operational feedback loop for whether stricter transport policy is breaking or being bypassed in the wild.
How TLS-RPT pairs with MTA-STS / DANE
TLS-RPT is the visibility layer that makes stricter transport policies manageable. MTA-STS and DANE tell senders what the receiving domain expects; TLS-RPT tells the receiving domain when those expectations were not met.
Without that feedback loop, teams can publish transport controls and still miss handshake failures, policy mismatches, or certificate problems affecting real senders.
Setting up the DNS record (HowTo)
TLS-RPT is published as a DNS TXT record that tells reporters where they can send aggregate transport-failure data. The operational part is not the syntax itself, but making sure the reporting destination is monitored by someone who can tie failures back to mail infrastructure changes.
Common report patterns
Most reports cluster around predictable issues: certificate mismatch, unreachable policy files, MX host changes, or senders that still cannot satisfy the published policy. Patterns over time matter more than one noisy report because they show whether the issue is isolated or systemic.
Tools that parse TLS-RPT
Raw reports are useful, but they become far more valuable when teams can aggregate and interpret them alongside MTA-STS, MX, and certificate posture. That is the gap tooling should close: from raw transport telemetry to an actionable explanation of what broke.
How to fix or implement TLS-RPT
A good implementation plan for TLS-RPT starts with inventory, not with copying a sample policy. Teams need to know which providers, applications, mail paths, or DNS owners are already in the flow before they tighten anything.
From there the safe pattern is consistent: publish the smallest defensible change, validate the result from the outside, and keep monitoring after rollout so the control does not quietly regress after a vendor or infrastructure change. CyberFurl helps most when that validation is tied back to live evidence from CyberFurl TLS-RPT check.
1
Baseline TLS-RPT on the live domain
Start by reading the exact DNS records, headers, or transport signals involved in TLS-RPT so you know whether the domain is merely configured or actually aligned with production traffic.
2
Publish or correct the control safely
Implement the smallest change that improves TLS-RPT without breaking legitimate senders, forwarders, or receiving paths. For email controls, staged rollout matters more than fast rollout.
3
Validate behavior end to end
Check that receivers, forwarding paths, and dependent services behave the way the policy claims they should. Configuration without real validation is how silent delivery regressions happen.
4
Monitor drift continuously
Keep watching reports, DNS changes, and sender inventory so TLS-RPT stays trustworthy after vendor changes, key rotation, or mail-routing updates.
Technical Architecture
SMTP TLS Reporting (TLS-RPT), defined in RFC 8460, provides a structured telemetry mechanism for domain owners to monitor the success and failure of encrypted email transit. When a sending Mail Transfer Agent (MTA) attempts to deliver an email to your domain, it relies on protocols like MTA-STS or DANE to ensure the connection is encrypted and the receiving certificate is valid.
Without TLS-RPT, if a sending MTA drops a message because of a certificate mismatch or a failed STARTTLS negotiation, the receiving domain has zero visibility into the failure. The email simply vanishes.
The architecture of TLS-RPT solves this by allowing the receiving domain to publish a DNS TXT record specifying a destination URI (usually an https:// endpoint or a mailto: address). Sending MTAs aggregate their connection statistics daily and deliver a gzip-compressed JSON report to this URI, detailing successful connections, failed connections, and the specific cryptographic or policy reasons for any failures.
Example of a TLS-RPT DNS record:
_smtp._tls.example.com. 3600 IN TXT "v=TLSRPTv1; rua=mailto:tls-reports@example.com"
DNS Flow
The DNS flow for TLS-RPT is deeply intertwined with the policy discovery mechanisms of MTA-STS and DANE:
Policy Discovery: A sending MTA (e.g., Gmail) prepares to send an email to user@example.com. It queries DNS for the MTA-STS TXT record (_mta-sts.example.com) or DANE TLSA records (_25._tcp.mx.example.com).
Reporting Discovery: Simultaneously, the sending MTA queries DNS for the TLS-RPT TXT record located at _smtp._tls.example.com.
Delivery Attempt: The sending MTA attempts to connect via SMTP and upgrade the connection using STARTTLS, validating the certificate against the discovered MTA-STS policy or DANE constraints.
Data Aggregation: Regardless of success or failure, the sending MTA logs the interaction (e.g., "Successful connection," "Certificate expired," "MTA-STS policy fetch failed").
Report Generation: Once a day, the sending MTA aggregates all interactions for example.com into a JSON document, compresses it, and sends it to the rua endpoint specified in step 2.
Trust Model
Unlike DMARC reporting, which is primarily concerned with who is sending email on your behalf, TLS-RPT is concerned with how others are connecting to your infrastructure.
The trust model here is one of cooperative diagnostic sharing between independent administrative domains. You trust that massive senders (like Google, Microsoft, and Yahoo) will accurately report their connection failures to you. Conversely, senders trust that by delivering these reports, receiver domains will proactively fix their broken certificates or misconfigured load balancers, thereby improving the global reliability of encrypted email transit.
Common Misconfigurations
Because TLS-RPT relies heavily on the correct implementation of underlying transport security protocols, misconfigurations often cascade:
Missing the _smtp._tls Prefix: A common mistake is publishing the TXT record at the root domain (example.com) or at _tls.example.com. It must strictly be published at the _smtp._tls subdomain.
Syntax Errors in the rua Tag: Forgetting the mailto: or https:// prefix in the rua tag will cause sending MTAs to silently discard the reporting destination. Example of a bad record: rua=tls-reports@example.com.
Ignoring the Reports: Publishing the record but routing the mailto: address to a blackhole or an unmonitored shared inbox. The JSON reports are intended for automated ingestion and parsing; humans cannot effectively read hundreds of raw, compressed JSON files daily.
Security Risks
Failing to implement TLS-RPT—or failing to act on its data—exposes the organization to severe operational and security risks:
Silent Mail Dropping: If your SSL certificate expires or your load balancer presents the wrong certificate chain, senders enforcing MTA-STS or DANE will immediately hard-fail the connection. Without TLS-RPT, this results in a catastrophic, silent inbound mail outage.
Downgrade Attack Blindness: If an active Adversary-in-the-Middle (AiTM) is stripping STARTTLS commands from your inbound traffic (a classic downgrade attack), TLS-RPT is the only mechanism that will alert you to the sudden spike in unencrypted connection attempts.
Policy Misconfiguration: When transitioning an MTA-STS policy from testing to enforce, TLS-RPT is critical. Enforcing without verifying via TLS-RPT that your MX records are fully compliant guarantees lost emails.
Compliance Impact
While TLS-RPT itself is a reporting mechanism, it is increasingly mandated as part of comprehensive email security frameworks:
Federal Mandates (BOD 18-01 Extension): While the original BOD 18-01 focused on DMARC, modernized federal guidance strongly recommends the implementation of MTA-STS and TLS-RPT to secure government communications against state-sponsored interception.
GDPR and Data Privacy: Ensuring that emails containing PII or sensitive customer data are strictly encrypted in transit is a core GDPR requirement. TLS-RPT provides the auditable proof that your transport encryption is functioning as designed.
Detection and Monitoring
TLS-RPT monitoring requires specialized tooling to ingest and visualize the daily JSON payloads from global senders:
JSON Parsing and Aggregation: Security teams must utilize platforms that can unpack the GZIP payloads, parse the RFC 8460 JSON schema, and aggregate the data into actionable dashboards (e.g., grouping failures by ASN, MX host, or specific error type).
Alerting on Failure Spikes: Monitoring must be configured to trigger immediate alerts if the ratio of failed to successful TLS connections suddenly spikes, which often precedes a major inbound mail outage.
Correlating with DMARC: Advanced security operations centers (SOCs) correlate TLS-RPT data with DMARC RUA data to gain a complete picture of both inbound transport security and outbound identity spoofing.
Best Practices
Deploy Alongside MTA-STS Testing: Never deploy MTA-STS in enforce mode without first deploying TLS-RPT. Run MTA-STS in testing mode for at least 30 days and monitor the TLS-RPT reports to guarantee zero failures before switching to enforcement.
Use Dedicated Ingestion Endpoints: Do not send TLS-RPT reports to a human-readable inbox. Use a dedicated https:// webhook endpoint or a specialized email parsing service designed to handle high volumes of machine-generated telemetry.
Regularly Rotate TLS Certificates: The most common cause of TLS-RPT failures is expired or mismatched certificates. Automate certificate renewal on your MX servers using protocols like ACME (Let's Encrypt) to prevent human error.
How CyberFurl Helps
Decoding cryptic JSON files to figure out why a partner's email server is dropping connections to your MX hosts is a massive operational burden.
Through the CyberFurl Email Intelligence suite, organizations gain instant, automated visualization of their global TLS-RPT telemetry. CyberFurl automatically ingests the daily reports from Google, Microsoft, and other major providers, translating raw JSON failure codes into plain-English diagnostics (e.g., "Certificate Expired on MX-2"). By continuously monitoring these trends, CyberFurl allows you to proactively identify and fix transport vulnerabilities before they result in dropped emails or intercepted communications.
Tools to check your TLS-RPT
Use the CyberFurl TLS-RPT check when you want to see the live signal on a real domain, and then step back to the See the email authentication feature page when you need the wider workflow around posture, monitoring, or remediation. That combination is usually much more useful than reading the standard in isolation.
TLS-RPT is not always mandated by law or by the protocol, but mature teams usually treat it as a baseline once the domain matters for customers, partners, mail delivery, or public trust. The real question is not “must I have it?” but “what risk am I carrying if I leave it weak?”
Where do reports get delivered?
The right next step is usually evidence first: inspect the live public behavior, identify the dependency or exposure that matters, and then decide whether to implement, tighten, monitor, or clean up. TLS-RPT is most useful when the answer is anchored in what production is actually doing rather than in documentation alone.
How big are TLS-RPT reports?
The right next step is usually evidence first: inspect the live public behavior, identify the dependency or exposure that matters, and then decide whether to implement, tighten, monitor, or clean up. TLS-RPT is most useful when the answer is anchored in what production is actually doing rather than in documentation alone.
Can I forward to Slack?
TLS-RPT can help, but only when the prerequisites and surrounding trust assumptions are also true. The safest answer is to validate the specific path you care about in production, because edge cases around forwarding, intermediaries, browser support, or vendor behavior are often where theory breaks down.
What is TLS-RPT?
TLS-RPT delivers daily reports about TLS failures on your inbound email — helping you debug MTA-STS and DANE issues. In practice, teams care about TLS-RPT because it changes a real trust boundary somewhere in the stack and gives them a concrete signal they can validate on the live domain or application.
Related reading
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