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

Microsoft’s new email security standards, including 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 reporting that helps identify delivery issues. Together, they reduce the risk of interception, downgrade attacks, and spoofing. 

Microsoft’s shift to new MX records enables these inbound protections. Only properly authenticated and encrypted messages are accepted, improving trust and deliverability.

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) discusses Microsoft’s latest email security updates and their real-world impact.

The conversation explains how MTA-STS enforces encrypted delivery and how TLS-RPT provides visibility into delivery failures. It also covers how DANE with DNSSEC work together to bind TLS certificates to your domain. Migrating to Microsoft’s new MX records makes it possible to enforce these protections on inbound mail, supporting stronger authentication and encryption standards. 

Timestamped Key Moments

• 00:00 — Introduction and why legacy email protocols fall short
• 02:26 — The evolving threat landscape including phishing, spoofing, and AI-driven attacks
• 04:04 — Risk assessment and identifying suspicious email
• 06:28 — Enforcing encrypted delivery with MTA-STS and TLS-RPT 
• 08:47 — DNSSEC and DANE and their role in certificate validation
• 13:34 — Reporting and troubleshooting with TLS-RPT and EasyDMARC
• 16:01 — Microsoft’s MX record update and inbound protections
• 18:28 — Building sender reputation and trust
• 20:45 — Detecting advanced attacks and maintaining compliance

What is MTA-STS and Why Does it Matter?

MTA-STS, or Mail Transfer Agent Strict Transport Security, requires email sent from your domain to use TLS encryption. If a secure connection cannot be established, the message is not delivered.

This prevents downgrade and man-in-the-middle attacks and ensures email is only delivered over encrypted connections. 

How TLS-RPT Improves Visibility and Troubleshooting

TLS-RPT provides domain owners with reports when email delivery fails due to TLS or MTA-STS issues. These reports are delivered in JSON format and explain where and why failures occur.

With this visibility, organizations can identify configuration issues quickly and improve mail flow reliability. 

What DNSSEC and DANE Strengthen Email Authentication

DNSSEC digitally signs DNS records to prevent tampering and spoofing. DANE uses those signed record to associate TLS certificates directly with your domain.

Together, these technologies help ensure that only valid, trust certificates are accepted during encrypted email delivery. 

Why Microsoft’s MX Record Update Matters

Microsoft’s move from protection.outlook.com to mx.microsoft enables inbound support for MTA-STS and DANE. This change allows organizations to enforce stricter security policies for incoming email. 

As a result, email authentication improves, encryption becomes enforceable, and sender reputation is strengthened. 

Advancing Microsoft Email Security Standards with Sourcepass MCOE

Email security requires ongoing attention, proper configuration, and regular review. Standards like MTA-STS, TLS-RPT, DNSSEC, and DANE help enforce encrypted delivery, strengthen authentication, and provide insight into mail flow issues before they disrupt operations.

Migrating to Microsoft’s new MX records unlocks inbound protections that support compliance and improve trust across the email ecosystem. Ongoing security awareness training and periodic assessments help organizations stay ahead of evolving threats.

If you have questions about deploying these protocols, auditing DNS configurations, or performing a security assessment, Sourcepass MCOE can help. Our team supports authentication configurations, security optimization, and alignment with current Microsoft best practices.

Subscribe to the Demystifying Microsoft podcast for continued insights, or connect with a Sourcepass MCOE expert 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