When signing up for Office 365 there are two really important decisions:

  1. Where will my tenant be homed (based on the region selected at sign-up)?
  2. What will my tenant be called?

The reason these are so important is because, once set, they cannot be changed.

I’ll write more about the home location of the tenant in a future post (why it matters in some ways, and why it doesn’t in others) but, for now, let’s look at the tenant name.

To explain what this is, when you sign up for Office 365, a new tenant is created and given a name in the form tenantname.onmicrosoft.com.

By default, users log on with username@tenantname.onmicrosoft.com and that becomes their email address too. Other domain names can be added to the tenant after which the user name can be changed accordingly, as well as the email addresses. The initial tenantname.onmicrosoft.com name can’t be removed though.

If you’ve added additional domains to the tenant, the only time you’ll see the underlying tenant name is in the URIs for SharePoint Online and OneDrive for Business which are tenantname.sharepoint.com and tenantname-my.sharepoint.com respectively.

Pick your name carefully. What seems a good idea today may not seem so good further down the road. Just as we picked Windows NT domain names in the past that caused challenges later, our Office 365 tenant name (which is actually your Microsoft Online Services tenant name) needs to be chosen with care. Personally, I’d avoid putting 365 in it as the scope is potentially much broader. companyname.onmicrosoft.com is probably about the safest bet, at least until your company merges with another company! Or you could go with something completely ambiguous like ABC123…

Further reading

About your initial onmicrosoft.com domain in Office 365.

[This is an edited version of a post that was originally published at markwilson.it]