HCW8001 – Unable to determine the tenant routing domain

As a consultant in messaging and collaboration I have created dozens of Exchange hybrid configurations that last years, ranging from Exchange 2010 to Exchange 2019.
Today we’ve run into an issue I have not seen before, the HCW8001 – Unable to determine the Tenant Routing Domain error:

Unable to determine the tenant routing domain

Note. In one of my earlier blogs Moving from Exchange 2010 to Office 365 somebody mentioned this specific error in the comments in September 2018.

When you click Learn more you are redirected to the following Microsoft page:
https://support.microsoft.com/en-us/help/3068010/unable-to-determine-the-routing-domain-for-the-cloud-organization-erro which states you have to enable Directory Synchronization using the following command:

Set-MsolDirSyncEnabled -EnableDirsync $true

Which of course we did, but no success.

Azure AD Connect was running fine, I checked the configuration (optional features) and found nothing strange and no errors were logged.

Optional Features

When checking the Microsoft Portal I could see Directory Synchronization was running:

Azure AD Connect

The tenant routing domain is typically something like <tenantname>.mail.onmicrosoft.com and this is set in Office 365 when installing Azure AD Connect. But when checking the Accepted Domains (in Exchange Online) this domain is not available:

Accepted Domains

There’s no way you can add this <tenantname>.mail.onmicrosoft.com domain manually (also not via the Microsoft Online Portal) so you are out of luck (I tried the Azure AD Connect server multiple times, but it didn’t work).

You can open a ticket with Microsoft Support or see if you can create a new tenant and start over again. Since this happens rarely I would be surprised you run into this again with a new tenant.


4 thoughts on “HCW8001 – Unable to determine the tenant routing domain”

  1. I am getting this same error on a new tenant. Do you know if I delete this new tenant and create another will I be able to use the same tenant name again?


    1. Hi, no I’m afraid that’s not possible. Once a name is given to a tenant that name is not available as long as the tenant is in Office 365. If you leave it there it will be deleted, but that will take a long time.


      1. Hey there, just wanted to report back that O365 support was able to resolve this issue for me my running some back end scripts.


  2. This was a simple fix. Just go into your tenant Exchange console and be sure both it and your on-premise Exchange have matching accepted domains. One of them will be the public domain, one will be the .onmicrosoft.com, and one will be the .mail.onmicrosoft.com


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