Securing Email Delivery in Microsoft 365 with MTA-STS and DNSSEC

Microsoft’s new email security standards (MTA-STS, TLS-RPT, DANE, and DNSSEC) are redefining how organizations protect email in transit. These protocols enforce encrypted delivery, validate sender authenticity, and provide actionable reporting, making it possible to prevent interception, downgrade attacks, and spoofing. 

The shift to Microsoft’s new MX records unlocks inbound protections, ensuring that only properly authenticated and encrypted messages reach their destination.

How to Secure Email Delivery in Microsoft 365 with MTA-STS, TLS-RPT, DANE, and DNSSEC

In this episode of Demystifying Microsoft podcast, Nathan Taylor (SVP, Global Microsoft Practice Leader at Sourcepass MCOE) explores the practical impact of Microsoft’s latest email security technologies. The discussion covers how MTA-STS enforces encrypted delivery, how TLS-RPT provides visibility into delivery failures, and how DANE with DNSSEC binds TLS certificates to your domain for stronger authentication. The migration to Microsoft’s new MX records enables organizations to enforce advanced inbound email protections, supporting stricter authentication and encryption standards that improve deliverability and trust.

Timestamped Key Moments

• 00:00 — Introduction: Why legacy email protocols are no longer enough
• 02:26 — The evolving threat landscape: Phishing, spoofing, and AI-driven attacks
• 04:04 — Risk assessment: Filtering legitimate vs. suspicious email
• 06:28 — Enforcing encrypted delivery: How MTA-STS and TLS-RPT work together
• 08:47 — DNSSEC and DANE: Binding TLS certificates to your domain
• 13:34 — Reporting and troubleshooting: Using TLS-RPT and EasyDMARC for actionable insights
• 16:01 — Microsoft’s MX record update: Unlocking inbound protections
• 18:28 — Building reputation and trust with multi-layered authentication
• 20:45 — Detecting sophisticated attacks and maintaining compliance

What is MTA-STS and Its Role in Secure Email Delivery?

MTA-STS (Mail Transfer Agent Strict Transport Security) is a protocol that requires email leaving your organization to use TLS encryption. If encryption cannot be established, the message is not delivered. This prevents downgrade and man-in-the-middle attacks, ensuring that only secure connections are used for email delivery. 

How Does TLS-RPT Solve Delivery and Security Issues?

TLS-RPT (Transport Layer Security Reporting) provides domain owners with reports on email delivery failures related to TLS negotiation, DNS issues, and MTA-STS problems. These reports, delivered in JSON format, offer clear visibility into where and why emails fail, enabling rapid troubleshooting and continuous improvement.

What Role do DNSSEC and DANE Play in Email Authentication?

DNSSEC (Domain Name System Security Extensions) digitally signs DNS records, preventing tampering and spoofing. DANE (DNS-based Authentication of Named Entities) binds TLS certificates to your domain, ensuring only valid, signed certificates are accepted for encrypted email delivery. Together, these standards provide end-to-end trust and prevent unauthorized interception.

Why is Microsoft’s MX Record Update Important?

Microsoft’s migration from protection.outlook.com to mx.microsoft unlocks inbound support for MTA-STS and DANE. This change enables organizations to enforce strict security policies for incoming email, improving deliverability and reputation with receiving servers.

Advancing Microsoft Email Security Standards with Sourcepass MCOE

Email security is a continuous process that relies on robust protocols, careful configuration, and regular review. Implementing standards like MTA-STS, TLS-RPT, DNSSEC, and DANE helps organizations enforce encrypted delivery, strengthen authentication, and gain visibility into mail flow issues before they impact business operations. Migrating to Microsoft’s new MX records enables advanced inbound protections, supporting compliance and improving trust across the ecosystem. Staying proactive with security awareness training and periodic assessments ensures your organization is prepared for emerging threats and evolving requirements.

If you have questions about deploying these protocols, want to audit your DNS setup, or need a security assessment tailored to your environment, Sourcepass MCOE can help. Our team offers support for configuring authentication records, optimizing security features, and aligning your setup with current best practices.

Subscribe to the Demystifying Microsoft podcast for ongoing insights, and reach out to connect with one of our Sourcepass MCOE experts or to schedule a Microsoft 365 email security assessment.

Explore the rest of the series:

• Part 1: How Microsoft 365 Secures Email with AI and Authentication

• Part 2: Fix Email Delivery and Spoofing with Better DNS Security

• Part 3: Email Security Best Practices with Microsoft Defender and EasyDMARC