Move mailbox data to user profile in 2nd domain forest

Super Contributor



- 1 tenant with AAD connect

- 2 domain forest (contoso.som,

- users in forest have 10GB mailbox data each

- need to move all users and mailbox data from to ( will be deleted)

- moved users should still use SMTP domain


What is the best way to address the migration requirement?



5 Replies

Is this related to the other thread, or a separate scenario? As in, what's the end goal here, move all the mailboxes to a single tenant in O365, or move them between the on-premises forests?

@Vasil Michev this is a separate scenario, target is to move users to new AD forest

So where are the mailboxes located, On-Prem or in ExO? If On-Prem, you will have to do some cross-forest moves in addition to the ADMT migration. If they are in ExO, you might be able to just to the ADMT part, then "match" the new user accounts against the cloud mailboxes.


Here are some guides to get you started:

@Vasil Michev any guide on how to match  the new user accounts against the cloud mailboxes.?

You'll probably have to use the hard-match method, as I imagine their immutableIDs will already be populated.