The Office 365 DNS Diagnostic and DNS configuration


This article describes the Office 365 DNS Diagnostic tool.

To use your own domain name with Office 365, you may have to manually set up as many as 10 DNS records at a third-party domain registrar website.

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.

The Office 365 DNS Diagnostic tool detects all the DNS records that are required by Office 365 services and identifies any known misconfigurations.


When to use the Office 365 DNS Diagnostic

DNS misconfiguration is the top cause of the issues that are listed in this section. We strongly recommend that you run the Office 365 DNS Diagnostic to identify these issues.

Exchange Online issues

  • Issues with mail delivery

    • Not receiving incoming mail from the Internet

    • Receiving nondelivery reports (NDRs)

  • Outlook client connectivity

    • Issues that involve connecting Outlook and Exchange Online

    • Autodiscover not working

Skype for Business Online (formerly named Lync Online) issues

  • Lync client sign-in issues

  • Instant messaging (IM) failure with federated or public IM Connectivity (PIC) contacts

  • Outlook Web App IM or presence issues

SharePoint Online issues

  • Accessing the public-facing website that uses your domain name

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.

  1. 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.

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    Note Make sure that the domain is added to the Office 365 portal ( 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

  2. 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.


For more information, go to the following Microsoft website:

Create DNS records for Office 365 when you manage your DNS records

Still need help? Go to Microsoft Community.

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