Change primary Email Domain in Exchange Admin Center

[albercuba]

Hello everyone,

soon our company name will change and our domain will change from @myolddomain.com to @mynewdomain.com

We do not have a hybrid environment, everything is in Azure and Microsoft 365

In our Microsoft 365 admin center I already added our new domain, it is healthy and in our Exchange admin center I added an alias with the new domain to all of our mailboxes after making some tests with a dummy account to test that emails sent to the new domain are being received without any problem.

When the day comes, that I have to move everything to the new domain. I have to go to the Microsoft 365 admin center and set the new domain as default.

The users will have to log out and back into their accounts.

Now the big questions are:

• How do I change the primary Email address in Exchange? Will it change automatically after I set the new domain as default in Microsoft 365 admin center?
• We use our windows accounts to log into our computers. Will I be able to log in as myuser@mynewdomain.com without any problem or do I have to use myuser@myolddomain.com ?
• In Microsoft 365 admin center, under Domains, I have myolddomain.onmicrosoft.com. Do I need to create a new one for mynewdomain.onmicrosoft.com, will it change automatically after I change the default domain or is this linked to the tenant name and can't be changed?
• Am I missing any other important step?

Thanks in advance

[#2]

Setting the domain as default doesn't affect existing users in any way. If you want to change their properties, such as UPN or primary SMTP address, you need to do so manually/via PowerShell. You can also use the bulk operations functionality in the UI, but that's only feasible up to a certain number of users.
As for the default .onmicrosoft.com domain, no, it will not change. And you shouldn't care about it. The only place that's visible is the SharePoint Online site collection address, but the ability to modify this is still not publicly available, afaik.

[#3]

@Vasil Michev Thanks. Then I guess I will have to create a new subscription and migrate the Tenant

[#4]

If the SharePoint domain matters that much, that's the only option currently. Doesn't hurt to open a support case and ask Microsoft just in case.