Send & Receive Issues

How to Fix PTR Record and Reverse DNS Email Errors (Error 550 5.7.363)

Adam Davis Sep 27, 2026 870 views

Question details

Users experience email delivery failures because the recipient's mail server detects a missing or incorrectly configured PTR record and reverse DNS setup.

How to Fix PTR Record and Reverse DNS Email Errors

Product: Microsoft 365
Device & OS: not provided
Scenario: Sending emails to recipients whose mail servers enforce strict reverse DNS checks to prevent spam.
Observed behavior: Email delivery fails and returns a bounce-back message with error code 550 5.7.363.

Before you start

Identify the hosting provider or Internet Service Provider (ISP) that manages your public IP address, as you will need their assistance to configure reverse DNS.

Solution 1Recommended

Contact Your ISP or Domain Hosting Provider

Since PTR records cannot be managed directly within Microsoft 365, you must request your IP provider to set up the reverse DNS lookup.

A PTR (Pointer) record resolves an IP address to a domain name, acting as the reverse of an A record. Strict mail servers require this match to verify the sender's identity. Microsoft 365 does not host the public IP addresses used for outbound routing of custom domains in this context, so the record must be created by the entity that owns your IP address.

Identify your IP owner

Determine whether your public static IP address is provided by your Internet Service Provider (ISP) or a third-party web hosting service.

Request a PTR record addition

Contact the support team of your ISP or hosting provider and request them to add a PTR record that points your public IP address to your email domain (e.g., mail.yourdomain.com).

Wait for DNS propagation

Allow up to 48 hours for the new reverse DNS configuration to propagate across global DNS servers before testing your outbound email delivery again.

Contact Your ISP or Domain Hosting Provider

Important: Your A record must already point to the same IP address for the reverse DNS lookup to function properly. Ensure both forward and reverse DNS match.

Solution 2

Contact Microsoft 365 Support for Assistance

If you are unsure how your outbound routing is configured or need help identifying the missing records, Microsoft 365 support can help analyze the bounce headers.

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Frequently Asked Questions

What is a PTR record and why is it required for email?

A PTR (Pointer) record maps an IP address back to a domain name, which is the exact opposite of an A record. Mail servers use reverse DNS lookups to verify that the sending server's IP address matches the domain it claims to represent, effectively filtering out spam and spoofed emails.

Can I add a PTR record directly in the Microsoft 365 Admin Center?

No, PTR records cannot be created or managed within the Microsoft 365 admin center or your standard domain registrar (unless they also host your IP). You must contact the ISP or hosting provider that physically owns and provides your public IP address.

How long does a reverse DNS update take to fix the 550 error?

Once your ISP adds or updates your PTR record, it can take anywhere from a few hours up to 48 hours for the DNS changes to fully propagate across global mail servers. You may continue to see the 550 5.7.363 error during this propagation period.

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