I have 7 Accepted domains on an Exchange server, 3 of which need to be fully migrated away to Office 365. The main Domain which has the SSL Certificate installed for the DNS names for the OWA, ECP, OAB, outlook anywhere ETC will be staying.
The three other domains will need to be put into the cloud and can't rely on anything from the exchange server once migrated.
I have completed a few single domain cut over migrations and understand the process needed.
Due to the Exchange server having to still serve the other 4 domains I'm at a bit of a loss with what to do.
Create three new Office 365 portals with the the domain verified
Create an endpoint to the Server (Cut over migration)
Create the Batch, (which will populate all users)
Manually remove any users that don't need to be synced accross
Repeat for the Delta syncs (incremental)
Once the mailboxes have populated and the delta sync has change the DNS Records to that of O365 on the domains, apply the licenses
Remove the batch