I have a question with Exchange on-prem (2016) to Exchange online migration with respect to In place hold and discovery.
Let us assume that there are 10 mailboxes in hold (Compliance management>In-Place eDiscovery & Hold) in on-prem. The user is planning to migrate the mailboxes in a phased manner. If 5 out of 10 mailboxes are migrated first, would that create a new hold in Exch Online EAC (Compliance management>In-Place eDiscovery & Hold) for these 5 mailboxes? When the next set of 5 mailboxes gets migrated, would it get added to the above created hold automatically or will it create a new hold?
If I understood the question right, it is if Holds are retained when you onboard a mailbox from on-prem to Office 365. When configured properly, eDiscovery searches in Hybrid can span premises, thus covering mailboxes on-prem as well as online. Thus eDiscovery can cover your migrated mailbox. Note that you cannot just goggle the In-Place hold switch in ExO anymore, and you need to use eDiscovery or Retention policies.