What Are MTA‑STS, TLS‑RPT and BIMI? Advanced DNS Settings for Safer Email and Stronger Brands

When teams ask why their perfectly legitimate emails still land in spam or why their logo does not show up in inboxes, the discussion quickly moves beyond basic SPF and DKIM. Today, serious email security and brand visibility depend on a second layer of DNS-based standards: MTA‑STS, TLS‑RPT and BIMI. These records do not replace SPF, DKIM and DMARC; they sit on top and tell other mail servers how strictly to enforce encryption, how to report problems, and how to display your visual brand when everything checks out.

In this article, we will walk through what MTA‑STS, TLS‑RPT and BIMI actually do, how they fit into your existing email setup, and what kind of DNS and hosting environment you need to deploy them safely. At dchost.com, we see the same questions repeatedly during security audits and deliverability reviews for domains hosted on our shared hosting, VPS, dedicated servers and colocation platforms. The goal here is to give you a practical, production-oriented view so you can plan, implement and maintain these records without breaking email delivery.

Where MTA‑STS, TLS‑RPT and BIMI Fit in the Email Security Stack

Before going deeper, it helps to put these three standards in context. Most organizations already know the first layer:

• SPF: tells the world which servers are allowed to send email for your domain.
• DKIM: cryptographically signs your emails so recipients can verify they were not altered.
• DMARC: says what to do when SPF/DKIM fail (monitor, quarantine, reject) and where to send reports.
• rDNS / PTR: links your sending IP back to a domain, which most providers now expect.

If you need a refresher, we have a detailed guide on how to set up SPF, DKIM and DMARC correctly on cPanel or a VPS, and another step‑by‑step article about improving email deliverability with SPF, DKIM, DMARC and rDNS.

Once that foundation is solid, you can add the second layer:

• MTA‑STS: ensures that SMTP connections to your domain are encrypted with TLS, and that they go to the right MX servers.
• TLS‑RPT: gives you aggregated reports when other providers cannot establish secure TLS connections to your mail servers.
• BIMI: lets inboxes display your verified brand logo next to messages that pass DMARC alignment and reputation checks.

Think of SPF/DKIM/DMARC as identity and policy, and MTA‑STS/TLS‑RPT/BIMI as encryption assurance and visual trust. Together, they reduce phishing risk, increase transport security, and help your real messages stand out in crowded inboxes.

MTA‑STS: Enforcing TLS Encryption for Your Domain’s Email

MTA‑STS (Mail Transfer Agent Strict Transport Security) is to SMTP what HSTS is to HTTPS. It lets you publish a policy saying: “Other mail servers must talk to my MX servers over TLS using valid certificates; if they cannot, they should fail instead of falling back to plaintext.” This protects you from downgrade attacks and some man‑in‑the‑middle scenarios on the email transport layer.

How MTA‑STS Works: DNS Record + Policy File

MTA‑STS has two key components, both of which you need to host correctly:

1. DNS TXT record at _mta-sts.example.com that announces the existence and version of your policy.
2. HTTPS policy file at https://mta-sts.example.com/.well-known/mta-sts.txt describing your MX hosts, policy mode and max age.

When another provider (say, a large mailbox provider) wants to send mail to [email protected], it:

• Looks up the _mta-sts.example.com TXT record to see if MTA‑STS is enabled and which version of the policy to use.
• Fetches the policy file via HTTPS from mta-sts.example.com.
• Checks if the MX records it will use match the hosts listed in the policy.
• Attempts an SMTP connection with TLS that validates against a trusted certificate for those MX hosts.
• Follows your policy mode to decide whether to deliver, fail, or only report problems.

MTA‑STS Policy Modes: none, testing, enforce

Your MTA‑STS policy file has a mode directive:

• mode=none: policy is published but not enforced; it is mainly for discovery and future use.
• mode=testing: providers can send TLS reports when something is wrong, but still deliver mail even if TLS fails.
• mode=enforce: providers must refuse to deliver mail if they cannot establish a secure TLS connection that matches your policy.

In real migrations we run at dchost.com, we almost always start with testing for a few weeks, monitor TLS‑RPT reports, fix misconfigurations, then move to enforce once we are confident.

Example: MTA‑STS Policy and DNS Record

Here is a simple policy file for a domain whose MX records point to mail1.example.com and mail2.example.com:

version: STSv1
mode: testing
mx: mail1.example.com
mx: mail2.example.com
max_age: 604800

The corresponding DNS TXT record at _mta-sts.example.com could look like this:

_mta-sts.example.com. 3600 IN TXT 'v=STSv1; id=20250101T000000;'

The id value is just a policy version string. When you change your policy file (for example, when adding a new MX host), you should also change this id so senders know they must refetch the policy.

Common MTA‑STS Pitfalls We See

When we audit domains hosted on our shared hosting, VPS or dedicated servers, the same MTA‑STS issues keep appearing:

• MX hosts in policy do not match real MX records: For example, the policy lists mail.example.com but DNS MX points to mail.eu.example.com. This causes enforcement failures.
• Missing or invalid TLS certificates: Your MX hosts must present certificates whose CN/SAN matches the hostnames in the policy, and they must be trusted (for example, issued by a recognized CA and not expired).
• Forgetting the HTTPS endpoint: Publishing the TXT record without hosting a valid mta-sts.txt file over HTTPS breaks the standard.
• Jumping straight to enforce: Putting mode=enforce in place before checking TLS‑RPT reports can cause legitimate mail to be rejected if any path is misconfigured.

If you are already familiar with DANE/TLSA for SMTP, you can combine both approaches. We have a separate article focused on a deeper dive into MTA‑STS, TLS‑RPT and DANE/TLSA for SMTP security, where we compare DNSSEC-based and policy-file-based methods.

TLS‑RPT: Seeing When TLS Fails for Your Domain

TLS‑RPT (SMTP TLS Reporting) is the visibility layer for MTA‑STS and opportunistic TLS. It lets other providers send you daily aggregate reports about TLS negotiation problems they encounter when trying to deliver mail to your domain.

Common problems surfaced by TLS‑RPT include:

• Expired or misconfigured certificates on your MX hosts.
• Unsupported protocol versions or cipher suites.
• DNS issues that prevent connecting to the advertised MX servers.
• Policy mismatches between MTA‑STS and real-world SMTP connections.

How TLS‑RPT Works in Practice

To enable TLS‑RPT, you publish a single DNS record at _smtp._tls.example.com. This record tells senders where to email their aggregate reports, usually in JSON format, compressed and attached. A typical flow:

1. Sender attempts to deliver mail to your domain over TLS.
2. If there is a TLS issue, it records the outcome (failure type, affected MX, counts).
3. Once per day, it bundles all incidents into a report and sends it to the email address from your TLS‑RPT record.
4. You (or your monitoring system) process these reports to detect trends and problems.

We usually recommend sending these reports to a dedicated mailbox like [email protected] or to a processing service capable of aggregating and visualizing them. The volume is similar to DMARC RUA reports, and they are not meant to be read manually every day.

Example TLS‑RPT DNS Record

Here is a minimal TLS‑RPT record:

_smtp._tls.example.com. 3600 IN TXT 'v=TLSRPTv1; rua=mailto:[email protected];'

You can list multiple addresses separated by commas:

_smtp._tls.example.com. 3600 IN TXT 'v=TLSRPTv1; rua=mailto:[email protected],mailto:[email protected];'

After publishing the record, give providers some time to pick it up. In our experience, large email providers typically start sending reports within 24–48 hours once they see you also have MTA‑STS or a significant volume of TLS traffic.

BIMI: Turning Email Authentication Into Visual Brand Trust

BIMI (Brand Indicators for Message Identification) uses DNS to tell participating mailbox providers which logo to display next to email from your domain. When combined with strong DMARC settings and good reputation, it turns your security investments into a visible trust signal for users.

However, BIMI is very strict about prerequisites. Many domains add a BIMI record and then wonder why nothing shows up. The answer is almost always: DMARC and reputation requirements are not fully met.

BIMI Requirements Before You Start

Before touching BIMI DNS, you should ensure that:

• DMARC is in enforcement with p=quarantine or p=reject, not just p=none.
• Alignment is correct: the domains used in From:, SPF and DKIM are aligned according to DMARC rules.
• SPF and DKIM pass consistently for the majority of your email streams.
• Your sending reputation is clean: you are not on major blocklists, and your spam complaint rates are low.
• Depending on the provider, you may need a Verified Mark Certificate (VMC) for your logo, especially for some large mailbox providers.

If you want to go deeper into DMARC analytics, forensic reports and BIMI tuning, we already covered advanced DMARC reporting and BIMI implementation in more depth. Here we will focus on how BIMI interacts with DNS and your hosting.

How BIMI Works: DNS TXT + SVG Logo

BIMI relies on a TXT record at default._bimi.example.com. This record points to an SVG logo file, and optionally publishes VMC details. The logo itself must be served over HTTPS from a stable, high‑availability location.

The flow looks like this:

1. Mailbox provider receives a message from [email protected].
2. It validates SPF, DKIM and DMARC alignment; if they pass and DMARC is enforced, it may look for a BIMI record.
3. It queries default._bimi.example.com for a BIMI TXT record.
4. If the record is valid and your reputation is good, it fetches the SVG logo from the l= URL, validates VMC if used, and caches the logo.
5. It may display the logo next to your messages in the UI.

Example BIMI DNS Record and Logo Hosting

A basic BIMI record without VMC might look like this:

default._bimi.example.com. 3600 IN TXT 'v=BIMI1; l=https://assets.example.com/bimi/logo.svg;'

If you are using a Verified Mark Certificate, you would add a a= tag pointing to the certificate:

default._bimi.example.com. 3600 IN TXT 'v=BIMI1; l=https://assets.example.com/bimi/logo.svg; a=https://assets.example.com/bimi/vmc.pem;'

Key hosting considerations for the logo:

• Use HTTPS with a valid TLS certificate; HTTP will not work.
• Serve from a reliable origin: a subdomain on your main site, a static asset server, or a CDN fronting one of your servers at dchost.com.
• Correct format: BIMI logos must be specific “SVG Tiny Portable/Secure” style files, not arbitrary SVGs. Many providers have validators.

Because BIMI queries are not as frequent as normal web traffic, hosting the SVG on the same VPS or dedicated server where you host your main site is usually fine, as long as you apply standard security hardening. If you are already using a CDN, you can place the BIMI logo on the same static asset domain.

The DNS Records You Need: Quick Reference

Let’s summarize the core DNS records involved in MTA‑STS, TLS‑RPT and BIMI:

• MTA‑STS TXT record
  • Host: _mta-sts.example.com
  • Value example: v=STSv1; id=20250101T000000;
• MTA‑STS policy host A/AAAA or CNAME
  • Host: mta-sts.example.com
  • Points to the web server that serves /.well-known/mta-sts.txt
• TLS‑RPT TXT record
  • Host: _smtp._tls.example.com
  • Value example: v=TLSRPTv1; rua=mailto:[email protected];
• BIMI TXT record
  • Host: default._bimi.example.com
  • Value example: v=BIMI1; l=https://assets.example.com/bimi/logo.svg;
• Supporting records (already needed but must be correct)
  • MX records pointing to your mail servers.
  • A/AAAA records for your MX hosts, with proper rDNS/PTR for sending IPs.
  • SPF, DKIM and DMARC records in healthy, enforced configuration.

If you are also sending email over IPv6, we strongly recommend checking your AAAA, PTR and SPF records for consistency. Our guide on how to deliver email reliably over IPv6 goes through PTR, HELO and blocklist issues that can silently hurt deliverability.

Shared Hosting vs VPS/Dedicated: Where to Host Policies and Logos

At dchost.com we see two common architectures: domains whose email is hosted on our shared hosting platform, and domains with custom mail stacks on VPS, dedicated servers or colocation. Both can support MTA‑STS, TLS‑RPT and BIMI, but the operational details differ slightly.

On Shared Hosting

On a typical shared hosting plan:

• Your MX records usually point to the provider’s cluster (for example, mail.yourdomain.com CNAME to a shared mail host).
• SPF and DKIM are often auto-managed by the control panel.
• You still fully control DNS for _mta-sts, _smtp._tls and _bimi subdomains.

To implement MTA‑STS and BIMI on shared hosting with dchost.com:

• Create a mta-sts.yourdomain.com subdomain in the panel and point it to your hosting account.
• Upload your /.well-known/mta-sts.txt policy file to the correct directory.
• Host your BIMI logo (SVG) under a stable URL like https://assets.yourdomain.com/bimi/logo.svg.
• Publish TLS‑RPT, MTA‑STS and BIMI TXT records via the DNS editor.

For most small businesses, this is enough. The key is to keep your panel-managed MX, SPF and DKIM in sync with any changes dchost.com support applies to the mail infrastructure.

On VPS, Dedicated or Colocation Servers

If you run your own mail server stack (Postfix, Exim or similar) on a VPS, dedicated server or colocated hardware at dchost.com, you have more responsibility but also more flexibility:

• You define the MX hostnames and their IP addresses.
• You manage TLS certificates for SMTP, often using Let’s Encrypt.
• You control how aggressively you adopt MTA‑STS enforcement.

Best practices we recommend to customers in this scenario:

• Use a dedicated FQDN for MX such as mx1.example.com, mx2.example.com, and ensure both DNS and certificates match those names.
• Automate certificate renewal (for example, via ACME) and monitor expiry so that MTA‑STS enforcement never breaks due to an expired TLS certificate.
• Keep policy changes in lockstep with MX changes: when adding a new MX host, update your MTA‑STS policy file and id field at the same time.
• Monitor TLS‑RPT reports and SMTP logs, ideally integrated with your central logging stack. If you already use Prometheus and Grafana on your VPS, it is straightforward to add alerts around TLS failure spikes.

For customers building more complex setups (multiple MX, backup MX, or split delivery between on‑prem and cloud), it can be useful to revisit your underlying architecture first. Our guide on email redundancy architecture with multiple MX, backup MX and split delivery covers how redundant MX strategies interact with DNS and what to watch out for.

Monitoring, Maintenance and Troubleshooting

Publishing these records is not a fire‑and‑forget operation. They are more like security policies in code: you need to review, adjust and monitor them over time.

Using TLS‑RPT and DMARC Reports Together

In a healthy environment, you should:

• Review DMARC aggregate (RUA) reports to see who is sending mail on behalf of your domain, whether SPF/DKIM pass, and whether alignment holds.
• Review TLS‑RPT reports to see where TLS negotiations are failing, which MX hosts or IPs are problematic, and whether certain providers have trouble connecting securely.

Correlating the two can highlight issues such as:

• New third‑party senders that have not been added to your SPF or DKIM configuration yet.
• Misconfigured or legacy MX entries still receiving traffic without proper TLS.
• Regional connectivity problems affecting specific providers or IP ranges.

In our experience, the first two to four weeks after enabling MTA‑STS and TLS‑RPT are the most informative. After that, you mainly watch for regressions: certificate renewals gone wrong, new MX records missing from policies, or changes in your DNS provider.

Typical Problems and How We Fix Them

Here are some of the issues we routinely diagnose for customers and how we approach them:

• Symptom: TLS‑RPT shows high counts of certificate mismatch errors.
  • Cause: The MX host in DNS is mail.example.com but the SMTP certificate is issued for mx.example.com.
  • Fix: Either update DNS MX to point to mx.example.com or issue a new certificate covering mail.example.com. Then update MTA‑STS policy accordingly.
• Symptom: DMARC reports show a large source failing SPF and DKIM; BIMI logo does not show.
  • Cause: A new CRM or marketing platform added without updated SPF/DKIM configuration.
  • Fix: Add the provider to your SPF record and configure DKIM on that platform, then revisit DMARC alignment. Only after DMARC is clean and p=quarantine/reject is safe does BIMI make sense.
• Symptom: Some providers intermittently fail to deliver with MTA‑STS in enforce mode.
  • Cause: Intermittent TLS handshake issues, outdated cipher suites, or load balancer misconfigurations on one of several MX hosts.
  • Fix: Use targeted SMTP tests and logs to find the faulty MX, fix TLS and handshake settings there, then confirm via TLS‑RPT that failures drop.

All of this is much easier if your underlying hosting is well tuned: current TLS versions, proper OCSP stapling, and modern cipher suites. If you want to revisit your TLS settings on the web side at the same time, our guides on TLS protocol updates and vulnerabilities and enabling TLS 1.3, OCSP stapling and modern ciphers on Nginx/Apache are a good companion.

A Practical Roll‑Out Plan for MTA‑STS, TLS‑RPT and BIMI

To avoid surprises, we usually suggest customers follow a staged approach:

1. Stabilize SPF, DKIM and DMARC
   • Make sure all legitimate senders are covered in SPF and DKIM.
   • Move DMARC from p=none to p=quarantine and eventually p=reject, using reports to clean up.
2. Prepare your infrastructure
   • Verify your MX records, hostnames and TLS certificates.
   • Decide where you will host mta-sts.txt and BIMI SVG/VMC files (shared hosting, VPS, static asset domain, etc.).
3. Enable TLS‑RPT first
   • Publish _smtp._tls TXT record with a dedicated reporting mailbox.
   • Wait a few days to see initial reports and ensure parsing/monitoring works.
4. Publish MTA‑STS in testing mode
   • Host mta-sts.txt with mode=testing, list all active MX hosts, and set a reasonable max_age (for example, 7 days).
   • Create the _mta-sts TXT record with an initial id value.
   • Monitor TLS‑RPT for at least two to four weeks, fixing any TLS or MX inconsistencies.
5. Move MTA‑STS to enforce
   • Once reports show a stable state and no systematic failures, change policy to mode=enforce.
   • Update the id in your _mta-sts TXT record to signal the change.
6. Introduce BIMI
   • Ensure DMARC is enforced (not p=none) and that your spam/complaint metrics are healthy.
   • Prepare a compliant BIMI SVG logo and, if needed, a VMC.
   • Host the logo (and VMC) on a stable HTTPS endpoint and publish the BIMI TXT record.
   • Give mailbox providers time to validate, cache and start showing the logo; this is not instant.

This staged approach avoids the common trap of deploying everything at once and then having to debug overlapping issues. It also fits well into a broader security and reliability program, where you are already handling TLS, DNS, backups and monitoring systematically. If you are in the process of modernizing your infrastructure anyway, our articles on practical VPS security hardening and 3‑2‑1 backup strategies complement the email-side work.

Conclusion: Turning DNS Into a Security and Brand Asset

MTA‑STS, TLS‑RPT and BIMI may look like “just a few more DNS records”, but in practice they mark a mindset change. Instead of treating DNS and TLS as static background settings, you start using them as active policy tools: forcing secure email transport, collecting machine‑readable visibility on failures, and rewarding strong authentication with visible brand presence in inboxes.

On the infrastructure side, you need three things for this to work smoothly: stable DNS, reliable HTTPS hosting for policy and logo files, and mail servers with correctly managed TLS certificates. That is where choosing the right environment at dchost.com matters—whether you run email on our shared hosting, operate your own SMTP stack on a VPS or dedicated server, or colocate your hardware in our data centers. We can help you design DNS, TLS and backup strategies that support these standards instead of fighting them.

If you are not sure where to start, a good first step is to audit your current SPF, DKIM, DMARC and MX configuration, then plan a staged rollout of TLS‑RPT, MTA‑STS and finally BIMI. From there, you can refine monitoring and reporting, and gradually make your email infrastructure both safer and more recognizable in your customers’ inboxes. When you are ready to align your domain, DNS, hosting and email under a single, consistent strategy, our team at dchost.com is here to help you design and run that stack end‑to‑end.