Migrating from one 365 tenant to another tenant.

We recently converted a few hundred users PCs from their old 365 tenant to our tenant (company purchase).

From the PC perspective, we had the users do the conversion of the machine (disjoin/join).  They followed a 50-step guide with pictures of what to do, had around 200 users do it themselves.  IT would remote in once in a while when something occurred that didn't match the document but was minimal overall.

CONVERSION SYNOPSIS

We the user add a local 'other users' account to the computer.  This account was given administrative privileges and allowed them to use this account to facilitate the switching from one 365 domain to another.  This conversion for us, resulted in NO data loss.  Our users were still able to access their old 365 tenant /user account and get data.  Prior to the migration, we had users export their browser bookmarks into a file on the computer which they could import upon conversion.

From a OneDrive and Outlook email perspective, we used a 3rd party cloud tool to migrate this data from one tenant to another.  We did develop procedure to do this all manually; however, the time and effort it saved us and our users was worth using. 

Once they added the local admin account, it was then logged into.  The account name was "conversion" in this example

They disjoined from the work/school domain 

When disjoined, MS has you do an account check to ensure you can log back into the computer. 
Users just used the local admin "conversion" account they created.

Computer is rebooted and the users log back into the local account

They re-add themselves to the new 365 account.

It's important that they use this option and not the top one.

Assuming you have MFA setup, they will be challenged to setup their MFA access

Once this authentication is working, they will then be prompted to JOIN the new tenant.

We used a sperate tool to migrate email and OneDrive, but it could be manually done, but its time consuming.

BitLocker keys transferred during this process

The original 365tenant user account was still on the machine and could be accessed.

Once users confirmed their data was done, they self-deleted the admin account and their old user account.

The actual conversion from one tenant to another only took about 30 minutes.  

We had contingency in place in case users had issues and needed to revert back to the original tenant, which they could, but it wasn't needed.