Changing an administrator’s default email address in Office 365

After your registered for Office 365, you need to choose a prefix for your “initial domain”. This prefix will be added to .onmicrosoft.com, giving you a username for your administrator with the format of myusername@prefix.onmicrosoft.com. Afterwards, you may want to change this logon to something else after you added your own domain, such as user@domain.com. But wait! When you want to change it, you realise that it’s impossible, and the dropdown box with the domains is deactivated:

Changing your own account’s login cannot be done!

The solution? Use a second admin account!

Sidenote: You don’t need to use a license for the second admin account, which can be just a temporary account.

Create a new user (e.g. called tempadmin), and assign him Admin rights while creating him. Once you log in as this other administrator and view the first admin’s profile, you can see that the previously grayed out user name selection can now be edited:

Make your change, save it, done!

The first administrator can then add the previously used email address as an alternative email address (e.g., if you used abc@xyz.onmicrosoft.com before, and abc@xyz.com afterwards, you can add the first email address to the account so that emails sent to either will be received).

Once you’re done, you should either delete the temp admin, or at least remove his admin privileges.