Questions about changing default domain in Office 365 tenancy

[OneTechBeyond]

Hello,

We're going to be changing domains and as such, will need to change our Office 365 tenancy default domain (i.e. from company.com to new-company.com).   We are doing 100% cloud hosted Office 365 (not hybrid with onsite domain controllers), so all apps are authenticating directly to Azure/Office 365.

I've added the new domain to our tenancy and configured all DNS entries properly so it's basically ready to go.   The questions I have are:

1. If I make the change in Setup -> Domains to make newdomain.com my default, will that impact any of my currently configured Active Users?   Or will their apps and accounts continue to function as normal until I explicitly set their account to use the new user@newdomain.com as their default username/email?  (*assume that I have already added the new email/username to their active account*)

2. After I manually change a user's username/email in Active Users to the new username@newdomain.com, will their native desktop Outlook 2016 app (and the mobile Outlook app) automatically reconfigure themselves to use the new username, after the Active User logs in with their new username@newdomain.com credentials?   How long does it usually take between changing the Active User's username/email before Outlook detects that a change has occurred?

[#2]

Hi @OneTechBeyond

You can change the UPN using the following articles https://support.office.com/en-us/article/change-a-user-name-and-email-address-in-office-365-fb5ac074... and https://docs.microsoft.com/en-us/powershell/module/msonline/set-msoluserprincipalname?view=azureadps...

After you change the UPN the users will ask to login again using the new UPN, the time may differ depending the app, Outlook, Web, Activesync, etc.

[#3]

Hello

1.) If you make domain changes just on the tenant, your users aren't impacted. If you change the UPN from the user, they will have changes.

2.) They have to re-login after the changes, and it will automatically get a new configuration. I can't tell you anything about the duration.