A few posts on this since it’s what I’m working on :)

It is possible to sync all your mailboxes from Exchange On-Prem to Exchange Online as a single batch, and then complete individual items – but it’s not obvious that this is even possible.

Normally if you start a migration, you can choose multiple mailboxes or use a CSV file to specify which accounts to start migrating – while specifying the option to manually complete the batch, so the actual migration happens when you want it to:

The problem is, once you’ve fixed any problems that arise and mailboxes are in a ‘synced’ state, there’s no visible way to complete a single mailbox – just the whole batch. That may not be what you want to do. You could work out a way to create a separate batch for every single mailbox you’re migrating, but there’s also a way to complete one mailbox at a time.

In PowerShell, once you’ve connected to Exchange Online, you can run the a command to see all the mailboxes syncing, and their status:

Get-MoveRequest

If a mailbox is ready to be finalised, it should have the status of ‘Synced’. This is different to the status of ‘Completed’, which occurs once the mailbox has been fully migrated across.

To trigger the completion of a single mailbox in a batch, use this PowerShell command:

Set-MoveRequest -Identity “mailbox name” -CompleteAfter 1

The mailbox will then do it’s final syncing and complete, without affecting the other jobs in the same batch. The -CompleteAfter parameter is supposed to set the delay before the request is completed in date/time format, but using the value ‘1’ seems to immediately trigger this.

Now you can do a single batch job, and selectively complete mailboxes as you choose – easy! 

(Note that there was an old method of doing the above by setting the variable SuspendWhenReadytoComplete to $false which no longer works)