Hi @VB
Based on my test, the cross-forest linked mailbox migration is similar to cross-forest user mailbox migration.
The major difference is that the AD accounts are already in the target forest (ABC.com), so there is no need to use the ADMT tool to migrate the accounts.
Source Forest: XYZ.com
Target Forest: ABC.com
The general steps would be:
1.Enable the MRS Proxy endpoint on EWS virtual directory for cross-forest mailbox moves
2.run the following command in ABC.com to covert the user to a mail enabled user
Enable-MailUser -identity <user name> -ExternalEmailAddress <email address in the source forest>
3.run the prepare-moverequest.ps1 script (under the path C:\Program Files\Microsoft\Exchange Server\V15\Scripts) to copy the Exchange related attributes to the local account in ABC.com
./Prepare-MoveRequest.ps1 -Identity <source mailbox name> -RemoteForestDomainController <source forest domain controller> -RemoteForestCredential (Get-Credential SourceForest\Administrator) -LocalForestDomainController <target forest domain controller> -LocalForestCredential (Get-Credential TargetForest\Administrator) -TargetMailUserOU <the target OU specified when using ADMT> -UseLocalObject
4.run the following command to move the mailbox
New-MoveRequest -Identity <the mailbox to move> -Remote -RemoteHostName <target exchange server name> -RemoteCredential (Get-Credential SourceForest\Administrator) -TargetDeliveryDomain <source forest>
Besides, there is also a workaround to migrate via Export/Import pst files.
The general steps would be:
1.create a new mailbox in ABC.com
2.export the old mailbox to a pst file in XYZ.com
3.import the pst file into the new mailbox
Here are several links which may be helpful:
via Exchange:
Procedures for mailbox exports to .pst files in Exchange Server
Procedures for mailbox imports from .pst files in Exchange Server
via Outlook:
Export or backup email, contacts, and calendar to an Outlook .pst file
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