8 thoughts on “Exchange Resource Forest and Office 365 – Part I”

  1. Hey Jaap, great series.. I suspect you mean the sentence “When this property has a value of “2” it is a lined mailbox, if it has a value of “1” it is regular mailbox.” be linked mailbox ?


  2. Hi Jaap, Need some info on a project that am working on. We are performing a AD cross forest with O365 cross tenant migration due to company splitting in to 2 entities.
    Source forest has exchange hybrid with 0365. Target forest is without any exchange environment. We are performing simple AD accounts & computers migration using ADMT and O365 mailboxes are being migrated through third party tool with o365 cross tenant capabilities. My question is primarily on the sequence that needs to be followed. What i have thought is below. Will it work ?
    1. Add target forest in as additional forest for sync in source AD connect configuration.
    2. Perform AD accounts & computers migration using ADMT.
    3. Once all the AD accounts & computers are migrated to target forest, perform cross tenant migration for O365.

    Can you please advise.


    1. Hi Ahmed,

      what do you want to achieve with step 1?
      My initial thought would be to configure an Exchange server in the target forest (hybrid server for management purposes), use ADMT to copy users and workstations to the target forest, use Azure AD Connect to sync with target O365 tenant and then use 3rd party tool to perform cross tenant migration.

      Cheers, Jaap


  3. Hey Jaap,

    So we have a customer that has a Account/Resource forest as you’ve described here. They have successfully migrated all their mailboxes to the cloud. setup adconnect etc.

    Now, they would like to remove the “Resource Forest” from their existing environment, and leave their account forest in place.

    How would they go about removing the resource forest? and leaving their account forest in place?

    If they did remove the resource forest what would happen to their user accounts in the account forest?

    Here is a better explanation:




    1. Hi Robert,
      as you already mentioned you need an Exchange server in the account forest to manage the Remote Mailboxes. The thing is, you need to move all Remote Mailboxes (i.e. Mail-Enabled Users) to the account forest. The good thing is, you already have all users accounts there, so it’s just a matter of moving (merging) all Exchange properties of the linked mailboxes into the account forest.
      Unfortunately I still have to figure out the most efficient way to do this (and write another blogpost in this series)


  4. Hey Jaap,

    Yes. Thats the issue.,

    so it’s just a matter of moving (merging) all Exchange properties of the linked mailboxes into the account forest.

    I thought we could just run the set-user command and unlink the mailbox, but i now chatting with you i dont know if that will work or not.

    Would something like this do:


    I am pretty sure you cannot just use a script and copy the exchange attributes as the GUID and SIDs etc would all be different.




  5. What about just using ADMT to migrate/merge the accounts from the resource forest to the account forest?

    All of this of course with the migration to office 365 already completed.




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