Email delivery in Microsoft 365 depends heavily on one critical DNS record: the MX (Mail Exchange) record.

If your MX record is misconfigured, emails may fail, bounce, or route to the wrong mail server.

In this guide, you’ll learn what an MX record is, how it works in Microsoft 365, how to check and configure it, and common mistakes admins should avoid.

This article pairs perfectly with Exchange Online Mail Flow Troubleshooting, because MX issues are one of the most common root causes of email delivery problems.

What Is an MX Record?

What-Is-an-MX-Record
MX Record

An MX record is a DNS record that tells the internet which mail server is responsible for receiving emails for a domain.

When someone sends an email to user@yourdomain.com, the sending mail server:

  1. Queries DNS for the MX record
  2. Finds the destination mail server
  3. Delivers the message to that server

Without a valid MX record, email delivery cannot happen.

💥 Fun Fact: Did you know that MX records were introduced in the 1980s? They’ve been quietly powering email delivery for decades, and yet, most people have no idea they exist! 🤯

How MX Records Work (Simple Explanation)

Think of an MX record as a postal address for email.

  • Domain: yourdomain.com
  • MX record: points to a mail server
  • Priority: decides which server is used first

Lower priority numbers are preferred.

Example:

0   yourdomain-com.mail.protection.outlook.com

10  backupmail.yourdomain.com

The server with priority 0 is tried first.

MX Record in Microsoft 365

When you use Exchange Online, Microsoft provides a default MX record for your tenant.

Example:

yourdomain-com.mail.protection.outlook.com

This value is unique to your tenant and must be configured exactly as provided in the Microsoft 365 Admin Center.

Where to Find Your Microsoft 365 MX Record

To find the correct MX record:

  1. Open Microsoft 365 Admin Center
  2. Go to Settings → Domains
  3. Select your domain
  4. View DNS records
  5. Copy the MX record value

Always copy the value directly — never guess or reuse another tenant’s MX record.

How to Configure MX Record for Microsoft 365

MX records are configured at your DNS hosting provider, not inside Microsoft 365.

Typical DNS providers:

Steps (generic):

  1. Log in to DNS provider
  2. Open DNS management
  3. Add or update MX record
  4. Set:

Host/Name: @

Value: Microsoft 365 MX record

Priority: 0

       5.Save changes

DNS propagation may take up to 24 hours but often completes within 4-6 hours.

How to Verify MX Record Configuration

After configuring the MX record, verify it using:

  1.Microsoft 365 Admin Center

  • Domain status should show Healthy
  • No DNS errors

 2.Online DNS tools

Search for:

MX:yourdomain.com

And output will come like mentioned in this image.

 

MX-record-example
MX Record Example


Ensure the result matches the Microsoft 365 MX record.

How MX Record Affects Mail Flow Troubleshooting

If emails are:

  • Not arriving at all
  • Bouncing immediately
  • Never appearing in Message Trace

  Always check MX first

MX issues occur before Exchange Online processes the email.

Best Practices for MX Records in Microsoft 365

Follow these best practices:

  • Use only one MX record for Microsoft 365
  • Set priority to 0
  • Remove old mail server MX records
  • Document MX changes
  • Verify MX after migrations

Frequently Asked Questions (FAQ)

Can I have multiple MX records?

Yes, but only one should point to Microsoft 365 in most scenarios.

Does MX affect outgoing mail?

No. MX only controls incoming mail.

How long does MX propagation take?

Anywhere from a few minutes to 24 hours.

Final Thoughts

The MX record is one of the most critical DNS records for email delivery in Microsoft 365.
Even with perfect Exchange Online configuration, a wrong MX record will break mail flow.

Understanding and verifying MX records should always be one of the first troubleshooting steps for any email issue.