Single on-prem AD forest Exchange migration to Multiple Office 365 tenants

[Newlife]

Hi Community, 

One of our customer has about 12 Exchange servers in single AD forest with 10,000 mailboxes. They've multiple organizations segregated by Organization Units (OUs),

Let's Say they've the below forest, 

On-prem AD

Exchange 2016 server

Organizations are segregated by OU1, OU2, OU3 etc. 

They'd like to migrate OU1 to M365 tenant 1 and OU2 to M365 tenant 2 and OU3 to M365 Tenant 3.

Question:

1. What is the best approach for this type of migration, having single AD forest and migrate the mailboxes from different OUs to different tenants?

2. Can we get this done with Hybrid or 3rd party migration?

Any guidance would be of great help! Many thanks!

[#2]

@Newlife 

Before having Hybrid Exchange, you need to setup a Hybrid Identity solution (AD Connect). You can only configure one Azure AD tenant in an Exchange Hybrid scenario by the limitation of AD Connect.

PST migration to the different tenants can be done but be aware that there are some limitations and not the most user-friendly migration. There are some third-party solutions to make it easier. 

Microsoft's way:

https://docs.microsoft.com/en-us/microsoft-365/compliance/importing-pst-files-to-office-365?view=o36...

[#3]

@Newlife 

Searching on the web, I found a Microsoft post related to Exchange to Office 365 Migration

https://gallery.technet.microsoft.com/exchange-office365-migration

You can check it out. It might help you to accomplish your job.

[#4]

You can start with this document:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-topologies

[#5]

@Newlife 

This may be the answer you are looking for

https://techcommunity.microsoft.com/t5/exchange-team-blog/september-2020-hybrid-configuration-wizard...