Need to delete in-place hold orphaned mailboxes in Exchange SE

Because the mailboxes are (or were) on In-Place Hold, they can’t be fully deleted until all holds are removed. In Exchange Server / Exchange Online hybrid scenarios, the key steps are:

1. Identify and remove any In-Place Holds
2. Remove any other holds (Litigation Hold, Purview retention, eDiscovery case holds)
3. Then delete/let Exchange delete the mailbox

Follow these steps in order.

1. Verify and remove In-Place Hold

In Exchange Server, In-Place eDiscovery searches are what apply In-Place Holds. A mailbox can’t be fully cleared while it’s still on hold.

• You can’t remove an In-Place eDiscovery search if it is still placing content on hold. You must first disable the hold:

    Set-MailboxSearch "<HoldName>" -InPlaceHoldEnabled $false
    Remove-MailboxSearch "<HoldName>"
  

  This is the supported pattern shown here:

    Set-MailboxSearch "Hold-CaseId012" -InPlaceHoldEnabled $false; Remove-MailboxSearch "Hold-CaseId012"
  

  After the hold is disabled and the search removed, the In-Place Hold is no longer protecting the mailbox.

If the original In-Place eDiscovery object was deleted in the wrong order and the mailboxes are now effectively “orphaned” from that search, ensure there are no remaining In-Place Holds referencing them (for example, by reviewing other mailbox searches and their SourceMailboxes values). If any still list these mailboxes, remove them from SourceMailboxes or disable the hold as above.

2. Remove other holds that can block deletion

If these mailboxes are (or will become) inactive mailboxes in Exchange Online, all types of holds must be removed before they can be permanently deleted:

• Microsoft 365 retention policies and labels
• eDiscovery case holds
• Litigation Hold
• In-Place Hold

From the Purview side, the documented sequence is:

• Remove the mailbox from any retention policies (static scope example):

    Set-RetentionCompliancePolicy -Identity <retention policy GUID without prefix or suffix> -RemoveExchangeLocation <identity of inactive mailbox>
  

• Remove the mailbox from any eDiscovery holds (see “Removing content locations from an eDiscovery hold” in the referenced article).
• Remove Litigation Hold from the mailbox if present:

    Set-Mailbox -InactiveMailbox -Identity <identity of inactive mailbox> -LitigationHoldEnabled $false
  

• Remove any legacy eDiscovery/In-Place holds using Invoke-HoldRemovalAction:
  1. Discover holds that still apply to the mailbox:

    Invoke-HoldRemovalAction -Action GetHolds -ExchangeLocation <identity of inactive mailbox>
  

  2. For each legacy eDiscovery hold (HoldId is a GUID, possibly with a “cld” prefix), remove it:

    Invoke-HoldRemovalAction -Action RemoveHold -ExchangeLocation <identity of inactive mailbox> -HoldId <hold ID>
  

The Purview guidance explicitly states that all holds and retention policies must be removed before items in Recoverable Items (and effectively the mailbox) can be deleted.

3. Delete or let Exchange delete the mailboxes

On-premises Exchange Server:

• When the associated AD user account is deleted, Exchange marks the mailbox for removal, even if it was on Litigation Hold or In-Place Hold. To retain data, the account should be disabled instead of deleted. Once all holds are removed and the account is deleted, Exchange will clean up the mailbox according to its normal retention.
• If a mailbox remains as a disconnected mailbox in a database, Update-StoreMailboxState can be used to update mailbox state and allow final cleanup:

    Get-MailboxStatistics -Database "<DatabaseName>" | foreach { 
        Update-StoreMailboxState -Database $_.Database -Identity $_.MailboxGuid -Confirm:$false 
    }
  

  After that, verify the user object is gone:

    Get-User <UserIdentity>
  

Exchange Online inactive mailboxes:

• Once all holds (retention, eDiscovery, Litigation Hold, In-Place Hold) are removed from an inactive mailbox, it is automatically marked for deletion and permanently deleted after processing.

Summary action plan for the “orphaned” In-Place Hold mailboxes

1. In Exchange Server, ensure no remaining mailbox searches have InPlaceHoldEnabled = $true for these mailboxes; disable and remove any that do.
2. In Purview/Exchange Online (if applicable), remove the mailboxes from all retention policies, eDiscovery holds, and Litigation Hold, and remove any legacy holds using Invoke-HoldRemovalAction.
3. Delete or disable the associated user accounts as appropriate; allow Exchange to mark the mailboxes for removal and complete cleanup, using Update-StoreMailboxState if needed for disconnected mailboxes.

References:

• In-Place eDiscovery in Exchange Server
• Create or remove an In-Place Hold
• Delete an inactive mailbox
• Delete items in the Recoverable Items folder for mailboxes on hold in eDiscovery
• Disable or delete a mailbox in Exchange Server
• In-Place eDiscovery in Exchange 2013