22 october 2025, 13:44
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The Final Piece of the Puzzle
Hello! Here is the third and final part of our short series on email security. If you’ve followed our two previous pieces on MTA-STS and DANE, you already know how email delivery can be both a wonder of engineering and a bit of a security minefield.
You’ve locked down TLS. You’ve taught your servers to enforce encryption policies. You even use DNSSEC and DANE for certificate validation. But one night, a dreadful thought wakes you up: how do I actually know it’s all working?
Luckily, there’s one tech aimed exactly at that: ensuring the consistency and stability of your email security setup. Here comes – you guessed it right – one more acronym!
TLS Reporting Steps In
TLS Reporting (TLS-RPT) is the final member of our modern email security trio. TLS-RPT doesn’t encrypt or enforce anything by itself. Instead, it watches, logs, and reports on whatever happens when your messages travel across the net. Where MTA-STS and DANE are the security guards, TLS-RPT is the one writing the incident report.
Even the best security setup can fail silently – and when it does, you’ll want to know before your customers notice. With TLS-RPT, your system can automatically do just that, and let you know before bad things happen.
The Problem: Blind Spots in Email Encryption
Transport Layer Security (TLS) is great… until it isn’t.
SMTP – the protocol email still runs on – was not designed for security. TLS encryption was thrown in later as an optional upgrade with the addition of the STARTTLS command. The keyword here is “optional”. If something goes wrong – a misconfigured certificate, an expired key, a missing policy – the connection just falls back to plaintext delivery. And you’d never notice.
That’s not just theory. Here’s how it plays out in the real world.
Your domain has a shiny new MTA-STS policy, but a small DNS typo sneaks in. Suddenly, your outbound emails can’t negotiate TLS with a partner’s server, and the system silently falls back to unencrypted transmission. Your message still gets there, but your compliance officer’s heart would skip a beat if they knew how.
Or imagine your DANE record points to a certificate that expired yesterday. The handshake fails as a result – and again, the fallback kicks in.
You see no bounce, no error, no alert. Your mail flows, but it’s not as secure as you think.
That’s the blind spot TLS-RPT was created to fix.
TLS-RPT in Context: The Team Player
TLS-RPT doesn’t do the encrypting – it does the reporting. It is the analytics layer that ties together your other email security tools:
- TLS handles encryption per se;
- MTA-STS says “TLS or no way”;
- DANE authenticates TLS certificates via DNSSEC;
- And finally, TLS-RPT collects and reports what’s actually happening.
If you like analogies: TLS is the lock; MTA-STS and DANE are the rules defining how that lock should be used; TLS-RPT is the security cam that tells you when the lock’s jammed.
Without TLS-RPT, you’re walking blind – encryption might fail, but you’d never know.
History and Adoption
TLS-RPT was standardized in RFC 8460 back in 2018, born out of a simple need: visibility.
Organizations were implementing MTA-STS and DANE, but they lacked feedback. If a policy misconfiguration or certificate issue caused delivery problems, there was no structured way to find out.
So, TLS-RPT was designed as the reporting companion to MTA-STS and DANE – a daily summary that tells you how TLS connections to your domain actually performed.
Adoption followed quickly with top email providers like Google, Microsoft, Yahoo, and Fastmail, all of which generate and send TLS reports. Today, most major ESPs either support it or are on their way there. For domain owners, that means the moment you publish a valid TLS-RPT record, reports will start landing in your inbox.
So, how does it actually work? Let’s peek under the hood.
Under the Hood: How TLS-RPT Works
When a remote server tries to deliver mail to your domain, it follows these steps:
- The sending MTA looks up your MTA-STS and TLS-RPT DNS records.
- It tries to negotiate a TLS connection (via STARTTLS).
- It logs the outcome – success, failure, downgrade, or policy violation.
- Once per day, it compiles a JSON-formatted report summarizing all that data.
- That report is sent to the address specified in your domain’s special DNS record.
Reports include stats on successful and failed connections, policy validation results, and hints about what went wrong – for example, “expired certificate”, “no STARTTLS support”, or “hostname mismatch”.
Think of TLS-RPT as a near real-time telemetry feed for your email transport encryption.
TLS-RPT Report: What’s Inside?
The reports themselves are provided in now-ubiquitous JSON format, which makes them easily readable for machines (and not too hard for humans).
Here’s what it may look like:
{
"organization-name": "example.com",
"date-range": {
"start-datetime": "2025-10-18T00:00:00Z",
"end-datetime": "2025-10-18T23:59:59Z"
},
"policies": [
{
"policy-type": "sts",
"policy-string": "v=STSv1; id=20251018"
}
],
"summary": {
"total-successful-session-count": 1456,
"total-failure-session-count": 12
},
"failure-details": [
{
"result-type": "certificate-expired",
"sending-mta-ip": "192.0.2.1",
"receiving-mx-hostname": "mail.example.com"
}
]
}
Each report gives you a 24-hour snapshot of how the other server sees your domain’s TLS posture. You’ll see who tried to connect, whether encryption succeeded, and what kind of failures occurred.
You don’t need to parse these manually – tools like Postmark, Dmarcian, or Google Postmaster can digest them into graphs and trends. But even a quick skim can reveal obvious issues like certificate mismatches or persistent STARTTLS failures.
Setting Up TLS-RPT for Your Domain
Setting up TLS-RPT is surprisingly simple. You just need to publish a DNS record that tells the world where to send reports.
Example:
_smtp._tls.yourdomain.com. IN TXT "v=TLSRPTv1; rua=mailto:reports@yourdomain.com"
Let’s unpack that:
- v=TLSRPTv1 is the version identifier (always this value);
- rua=mailto:reports@yourdomain.com is the address where reports will be sent.
Once this record is live, any mail server supporting TLS-RPT will start sending you daily JSON summaries.
Best practices for TLS-RPT include:
- Use a dedicated mailbox for reports (e.g., tls-reports@yourdomain.com).
- Set up a rule to automatically archive or forward them to a parsing tool.
- Monitor trends, not individual events – you’re looking for repeated patterns or spikes in failure rates.
If everything is healthy, expect a steady stream of “all good” reports. But when something breaks – say, your certificate expires or your MTA-STS policy fails – the reports will flag it fast.
Troubleshooting and Common Pitfalls
Simple as it may be, there are a few things that can trip you up:
- No reports arriving? Double-check your DNS record syntax and TTL. Also ensure the receiving mailbox is working and doesn’t block attachments.
- Reports piling up? These aren’t to be stored forever. Use a parser to manage them, delete all “ok” reports after adding a checkmark in your logs.
- Confusing error types? Look for patterns. One failure per week usually means nothing. Ten identical ones daily? That’s a misconfig.
And remember: TLS-RPT doesn’t fix anything by itself. It just gives you the data you need to fix it – or to verify that your MTA-STS or DANE deployment is doing its job.
Wrapping It Up: The Big Picture
With TLS-RPT, the circle is complete.
Across this series, we’ve looked at three key technologies that secure the highway your emails travel on:
- TLS – encrypts the communication between mail servers.
- DANE – uses DNSSEC to verify that the certificate is truly yours.
- MTA-STS – enforces encryption rules to prevent downgrades.
- TLS-RPT – reports what’s actually happening out there, day by day.
If we go back to the analogy: TLS is your lock; DANE and MTA-STS are the blueprints and safety rules for how that lock must be used; and TLS-RPT is the security camera that tells you when the lock is jammed or someone’s forcing it.
Having all these in place, your email infrastructure isn’t just secure – it’s observable. You’re not guessing whether encryption works or not; you can prove it.
In the end, that’s what real security is about: not blind trust, but visibility, verification, and confidence that your messages make it safely to their destination.
And that wraps up our three-part series on email transport security – from securing the line, to locking down the rules, to watching it all in action.
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