Exchange 2019 - Splitting a public mailbox into multiple mailboxes.

Copper Contributor

Hello everyone,

we would like to migrate to M365, but back then only one mailbox was created for the public folders, and now that mailbox has a size of 240GB.

Now I want to split the public folders across multiple mailboxes using the script Move-PublicFolderBranch.ps1. This works fine without any major issues.

However, it still remains at 240GB in the mailbox.

Is there a way to clean up or perhaps change the primary hierarchy to another mailbox so that I can delete the original mailbox after the move?

Thank you in advance.

Best regards,

Felix Merkel

2 Replies
best response confirmed by Felix63110 (Copper Contributor)

Hi @Felix63110,

To split a public mailbox in Exchange 2019 and migrate the contents to multiple mailboxes, you can follow these steps:

1. Create new mailboxes: First, create the new mailboxes where you want to move the public folder contents. You can use the Exchange Admin Center (EAC) or Exchange Management Shell (EMS) to create these mailboxes.

2. Assign permissions: Assign the appropriate permissions to the new mailboxes to ensure they have access to the public folder content. You can assign permissions using the EAC or EMS.

3. Use the Move-PublicFolderBranch.ps1 script: As you mentioned, you can use the Move-PublicFolderBranch.ps1 script to move the public folder content from the original mailbox to the new mailboxes. Make sure to follow the instructions and syntax provided by the script.

4. Verify the move: After running the script, verify that the public folder content has been successfully moved to the new mailboxes. Ensure that all necessary data is present and accessible.

5. Update the primary hierarchy: Once you have confirmed the successful migration of public folder content, you can update the primary hierarchy to point to one of the new mailboxes. The primary hierarchy is the root folder that holds the public folder structure. You can use the Set-Mailbox cmdlet in EMS to update the primary hierarchy. For example:

Set-Mailbox -Identity "PublicFolderMailbox01" -DefaultPublicFolderMailbox "NewPrimaryHierarchyMailbox"

Replace "PublicFolderMailbox01" with the name of the mailbox containing the primary hierarchy, and "NewPrimaryHierarchyMailbox" with the name of one of the new mailboxes.

6. Test and cleanup: Test the access to public folders from client applications to ensure the new primary hierarchy is functioning correctly. If everything is working as expected, you can delete the original mailbox.

Before proceeding with any changes or deletions, ensure you have a proper backup and follow the necessary precautions to protect your data. It's also recommended to test these steps in a non-production environment or with a backup to avoid any unexpected issues.

Kindest regards


Hi Leon,

Thank you!
I changed the DefaultPublicFolderMovedItemRetention from 7 days to 1 day and will check it tomorrow.
If this doesn't work, I will change the hierarchy.

Best regards