Securing Email in Transit with MTA-STS, TLS-RPT, and DANE 

Attackers don’t just target users anymore. They exploit the gaps in the infrastructure that moves email across the internet. Encryption in transit was once optional, but that’s no longer sufficient when compliance, privacy, and reputation are at risk.

How Microsoft’s MTA-STS, TLS-RPT, and DANE Standards Strengthen Email Security Beyond SPF, DKIM, and DMARC

Part 4 of our podcast explores advanced standards like MTA-STS, TLS-RPT, and DANE. These protocols strengthen email delivery, provide visibility into failures, and help ensure end-to-end trust.

Microsoft is now enabling support for modern transport-layer protections such as MTA-STS, TLS-RPT, and DANE. These standards secure the delivery path itself, helping prevent downgrade attacks, man-in-the-middle interception, and integrity failures.

Think of it this way: if SPF, DKIM, and DMARC verify the sender’s identity, these newer standards confirm that the message arrived securely.

MTA-STS and Encrypted Email Delivery

Mail Transfer Agent Strict Transport Security (MTA-STS) ensures that outbound email from your organization uses TLS encryption. If encryption fails, the message doesn’t send. This eliminates silent downgrades to plaintext and strengthens compliance and privacy protections.

What IT professionals should know: 

• DNS acts as the control plane. You’ll publish an MTA-STS TXT record to define your policy.
• Microsoft 365 already supports outbound MTA-STS enforcement.
• To enable inbound protection, domains must update their MX records to Microsoft’s new mx.microsoft endpoints.

Bottom line: this closes the door on attackers intercepting or downgrading your mail mid-flight. 

TLS-RPT Helps you Diagnose Encryption Failures

TLS Reporting (TLS-RPT) works alongside MTA-STS to provide visibility when encryption fails during email delivery.

• Reports are delivered in JSON format, detailing which servers failed, why they failed, and how frequently.
• When paired with tools like EasyDMARC, these reports become actionable through dashboards that help interpret the data.
• Similar to DMARC, TLS-RPT can be deployed in a “reporting only” mode before enforcing stricter policies.

Without TLS-RPT, email delivery issues are a mystery. With it, you finally have the data to fix misconfigurations before they disrupt business. 

DANE and DNSSEC Secure Email with Cryptographic Trust

DANE (DNS-based Authentication of Named Entities) takes encryption further by ensuring only trusted TLS certificates can secure your email. Combined with DNSSEC, it cryptographically signs DNS records so attackers can’t tamper with them. 

• DNSSEC is step one. You can enable it at your registrar. Cloudflare, Route 53, and GoDaddy all support it.

• DANE builds on DNSSEC by binding TLS certificates to your domain so only valid, signed certs are accepted.

• Microsoft’s MX shift makes this possible. The move from protection.outlook.com to mx.microsoft enables inbound support.

This means even if someone tries to fake encryption, it won’t pass validation. 

Why This Matters Now 

Taken together, MTA-STS, TLS-RPT, and DANE don’t just make email more secure. They make it more reliable. They provide: 

• End-to-end trust that your mail hasn’t been intercepted or downgraded. 
• Clear reporting to troubleshoot issues before they hit the business. 
• A stronger reputation with receiving servers, improving deliverability for legitimate mail. 

Where IT Leaders Should Start 

1. Audit your current DNS setup. Confirm that you control registrar accounts and have DNSSEC enabled.
2. Plan your migration to Microsoft’s new MX records to unlock inbound protections. 
3. Turn on TLS-RPT reporting before enforcing MTA-STS. This helps you identify what will break.
4. Layer in EasyDMARC or similar tools for visibility across SPF, DKIM, DMARC, and TLS. 

Strengthen Email Trust with Sourcepass MCOE

Part 1 explained why trust is the new battleground. Part 2 laid the foundation with SPF, DKIM, and DMARC. Part 3 introduced Microsoft Defender as the bouncer at the door. Part 4 focused on hardening the infrastructure to ensure no one tampers with your mail in transit.

For Microsoft 365 customers, these capabilities are available now. The sooner you configure them, the sooner your organization builds a reputation for being secure in practice, not just on paper.