Reverse DNS

Question

my reverse DNS does not match with my sending domain - how do I fix

Answer 1

Hi RossG,

This error typically indicates that the PTR (reverse DNS) record for your sending IP address does not match the hostname used by your mail server when sending email. Many mail providers use this check as part of their anti-spam filtering, and a mismatch can negatively affect email delivery.

To resolve the issue:

1. Identify the public IP address that is sending your email.
2. Check the current PTR (reverse DNS) record for that IP address.
3. Ensure the PTR record resolves to the same fully qualified domain name (FQDN) used by your mail server, such as mail.contoso.com.
4. Verify that the hostname returned by the PTR record also has a matching A record that resolves back to the same IP address.
5. If the PTR record is incorrect, contact the provider that owns the public IP address (ISP, hosting provider, cloud provider, etc.) and request that they update the reverse DNS entry.
6. Confirm that SPF, DKIM, and DMARC are configured correctly for your sending domain to improve mail authentication and deliverability.

For example:

• Sending domain: contoso.com
• Mail server hostname: mail.contoso.com
• PTR record for the sending IP: mail.contoso.com

If the PTR record instead resolves to a different hostname (for example, server123.hostingprovider.com), you may encounter reverse DNS mismatch warnings.

In general, resolving this issue typically requires ensuring that the IP address used to send email has a PTR (reverse DNS) record that points to the correct mail server hostname, and that the same hostname is used by the mail server when establishing SMTP connections. If you do not manage the public IP address yourself, you may need to contact your ISP, hosting provider, or email service provider to update the reverse DNS record.

If you require more direct assistance after confirming the details with your domain provider, the most effective next step is reaching out to your IT admin and ask them to use their admin credentials to submit a support request through the Microsoft 365 Admin Center.

Microsoft also provides customer service phone numbers based on your region. You can find the appropriate contact number here: Customer service phone numbers - Microsoft Support 

This route ensures that a Microsoft support engineer can initiate a remote session to investigate backend configurations, run advanced diagnostic tools, and, if necessary, escalate the case to specialized teams with access to internal systems and logs. These backend resources are essential for resolving issues that go beyond what’s visible in the user interface.

As community moderators, we’re here to guide you, but due to privacy and security limitations, we don’t have access to the backend tools required for a full resolution. For this reason, contacting Microsoft Support via the Admin Center is the most secure and efficient way forward. 

I hope this helps you resolve the issue quickly. I’m glad to assist and truly hope the information provided has been useful. Please feel free to reach out anytime if you need further assistance.  

If you find my post helpful, kindly consider marking it as the accepted answer. Doing so can assist others in the community who may have similar questions in finding solutions more quickly.  

Thank you for your kindness and contributions to the forum. 

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