After having performed dozens of on-premise Exchange to Office 365 Hosted exchange migrations, the path of least resistance for these email migrations is to use a combination of tool.
Microsoft Office 365 has a built-in migration tool we have tested it and it has lots of bugs and has not worked very well especially if your email accounts have multiple domains (i.e., joe@lme.com – joe@lmes.com – joe@lmeser.com) so it is recommended to use Azure AD Connect (also know as Entra Connect) to easily import all of your users into Office 365 and then pause Entra AD connect so that the users are cloud-only.
After the sync/connect is paused, use the 3rd party tool BitTitan MigrationWiz to import all of the data. You can then resume the Azure AD connect so that the password sync between your Active Directory server in your exchange stays functional
Step 1 – Install and Run Azure AD – (aka, Entra Connect) on your Active Directory server
Download the Azure AD Connect tool by clicking here
Use Express Settings, log in with your domain admin credentials, and then log in to Azure AD with your global admin Office 365 credentials. You can leave everything else to defaults and stat the sync (it will only import the users and not affect email or users in any way) – Here is a deep dive if you want a more thorough Azure AD Connect walkthrough
After a few minutes, you should see the users in Office 365 with a server next to their names (indicating they are On-Prem users and not Cloud users)
We want them to be cloud users, so we have to pause the Azure AD connect service
Follow this blog post to pause the Azure AD sync
Once they are cloud-only users (shown in the image), you can now move to the email migration section.
