DNS Records for Exchange Online
Introduction to Exchange OnlineDNS Records for Exchange Online

DNS Records for Exchange Online

20 mins

Understanding the Concept

DNS records are critical for Exchange Online mail flow and service discovery. The MX record directs inbound mail to Exchange Online, while SPF, DKIM, and DMARC records authenticate outbound mail to prevent spoofing.

Autodiscover CNAME records enable automatic client configuration in Outlook, eliminating the need for manual profile setup. The autodiscover endpoint helps clients find the correct server settings.

DKIM (DomainKeys Identified Mail) adds a digital signature to outbound messages, while DMARC defines what happens when SPF or DKIM checks fail, providing comprehensive email authentication.

Key Points

•MX record points to *.mail.protection.outlook.com
•SPF record includes spf.protection.outlook.com
•Autodiscover CNAME points to autodiscover.outlook.com
•DKIM requires two CNAME records (selector1, selector2)
•DMARC record defines policy for authentication failures
•TXT records are used for domain verification

Email Authentication Flow

1

SPF Check

Verify sender IP against DNS TXT record

2

DKIM Verify

Validate digital signature on message

3

DMARC Policy

Enforce policy based on SPF/DKIM results

4

Delivery

Accept, quarantine, or reject message

Why This Matters

Incorrect DNS configuration is the number one cause of mail delivery failures in Exchange Online. Proper SPF, DKIM, and DMARC records are essential for email deliverability and preventing your domain from being spoofed.

Common Mistakes to Avoid

✗Having multiple SPF records instead of a single combined record
✗Not enabling DKIM signing after adding CNAME records
✗Setting DMARC policy to reject before monitoring with none/quarantine first

Interview Discussion Points

💡Explain the complete email authentication chain (SPF → DKIM → DMARC)
💡Describe how to troubleshoot mail delivery failures related to DNS
💡Discuss the importance of autodiscover for Outlook client configuration

MS-203 Exam Tips

📝Know the exact format of SPF, DKIM, and DMARC DNS records for Exchange Online
📝Understand how MX record priority affects mail routing in hybrid environments
📝Be able to identify correct autodiscover CNAME configurations

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