Moving from Exchange on prem to Exchange online - how to migrate?

[Niklas_Nyberg]

Hi

We have all our mobile phones registrated in Intune and connect to our on prem Exchange server with the Outlook app via an Outlook app config.

Now we want to migrate the mailbox to Exchange online and trying to change the app configuration from Basic authentication to Modern Authentication.

A test mailbox is migrated to Exchange Online and we apply the new Outlook app config with Modern Authentication (Username attribute and Email address attribute from AAD are both UPN) but it doesn't work. Got a  login prompt in Outlook on the phone but cant login.

Is it possible to do this migration without removing the account in the Outlook app? If I remove the account in Outlook it will find the new 365 account and it all work but we have 1000+ phones and I dont want to tell the users to remove the account if its not necessary.

[#2]

Unfortunately, I haven't found any other way to do it either. I actually had to explore exactly this scenario recently, and my findings are the same: after configuring Outlook Mobile through app configuration, you can't change it without removing the account from the device.

Adding a new account also works, if I remember correctly, but that still requires manual removal of the old account.

[#3]

Got a solution from Microsoft to use "Hybrid Modern Authentication" to solve the migration. Is it someone who has any experiance from this?