Office 365 DNS Diagnostic

August 23, 2020 Dellenny

If you are using your own domain in Office 365 you may face issues

DNS misconfiguration is one of the top issues that are experienced by Office 365 customers. If DNS records are missing or are configured incorrectly, you may likely experience issues with mail flow issues, Outlook connectivity issues, Lync sign-in issues, or federation issues with external instant messaging (IM) providers.

Microsoft has released a tool to help troubleshoot the issues:

Per Microsoft document

How to use the Office 365 DNS Diagnostic

You can run the Office 365 DNS Diagnostic on any computer that has Internet access. The tool queries the Office 365 DNS records from the computer’s default DNS server by using Nslookup.exe and then detects DNS misconfigurations. However, it doesn’t collect any data that is specific to the computer on which it is running.

On the O365 Customer Domain Name page of the Office 365 DNS Diagnostic, type your domain name. The tool checks the DNS records for the domain.

Note Make sure that the domain is added to the Office 365 portal (http://portal.office.com) and that the domain is verified. If you haven’t verified your domain yet, go to the following Microsoft website:Add your domain to Office 365
On the Exchange Deployment Scenario page, select the scenario that applies to you. The options are Cloud Only and Co-exist/Hybrid.

If you have multiple domains, be aware that the scenario that you select applies to the domain that you entered in step 1.
- Select Cloud Only if all mailboxes of that domain were moved to Office 365.
- Select Cloud Only if you don’t have any Exchange Online mailboxes that use the domain.
- Select Co-exist/Hybrid if some mailboxes are hosted in the on-premises Exchange Server environment and some mailboxes are hosted on Exchange Online.