About 12 users have an on-prem source and target mbx. We could export the target mbx to a pst and import it into the source mbx, migrate/match/merge and sync all the mail to O365. But the customer is asking if we can do a native move of the target mbx to the O365 tenant, then merge the source mbx with the target mbx in O365.
I was able to migrate and merge a mbx from the on-prem source Exchange to a target mbx in O365. The target mbx was moved from the target on-prem Exchange to O365 prior to the source to target migration.