Error when you use the MOSDAL Support Toolkit to perform a DNS lookup to retrieve the Host (A) record in Office 365: "Host name could not be resolved in DNS"

When you use the Microsoft Online Services Diagnostics and Logging (MOSDAL) Support Toolkit to perform a Domain Name System (DNS) lookup to retrieve the Host (A) record of a provided host name in a Office 365, the Microsoft Exchange Remote Connectivity Analyzer tool displays the following error message if the DNS lookup operation doesn't return an IP address:

To resolve this issue, do one of the following things, as appropriate for your situation.

• Use Nslookup to check whether the Host (A) record exists on the DNS server. For more information about how to do this, go to the following Microsoft TechNet website:
  
  To verify A resource records exist in DNS
• If the CNAME record for the Autodiscover service is incorrect, you can manually add or change the host record. For more information about how to do this, go to the following Microsoft website:
  
  Use a CNAME Record to Enable Outlook to Connect
  Note If your external DNS zone is hosted by a third-party provider, you may have to contact that company or use custom tools to make these DNS modifications.
• If the DNS record for the Autodiscover service is set up incorrectly, you can check whether the Autodiscover service is working correctly. For more information about how to do this, click the following article number to view the article in the Microsoft Knowledge Base:
  
  2404385 Outlook can't set up a new profile by using Exchange Autodiscover for an Exchange Online mailbox in Office 365
  
  
  

This issue occurs if one or more of the following conditions are true:

• The Host (A) record doesn't exist on the DNS server.
• The CNAME record for the Autodiscover service is incorrect.
• The Autodiscover DNS record is set up incorrectly.

For information about how to troubleshoot DNS, go to the following Microsoft website:

Still need help? Go to the Office 365 Community website.