Microsoft 365 retains a deleted mailbox for 30 days in a soft deleted state. Restore the user account in the Microsoft 365 admin center or execute Undo-SoftDeletedMailbox in Exchange Online PowerShell. After 30 days the mailbox is permanently deleted. Placing a hold before deletion creates an inactive mailbox that retains the content.
Your user account was deleted and the mailbox went with it. Microsoft documents a 30 day window and the steps that restore the mailbox inside it.
Facts follow the Microsoft Learn article on deleting and restoring user mailboxes in Exchange Online. Microsoft describes Exchange Online recovery in that article and gives no third party backup restore.
What are the Mailbox Deletion States?
| State | Recoverable? | Example |
|---|---|---|
| Soft deleted | Yes, for 30 days | User deleted in the admin center or with Remove-Mailbox and still in the Entra recycle bin |
| Soft deleted with hold | Yes | Entra user hard deleted but a Litigation Hold or eDiscovery hold existed before deletion |
| Hard deleted | No | Soft deleted for over 30 days or removed with the PermanentlyDelete switch |
How to Restore From the Admin Center?
Deleting a user account deletes the mailbox. Restore the user account on the Deleted Users page within 30 days. Microsoft states you cannot use the Exchange admin center to delete or restore user mailboxes.
How to Restore With PowerShell?
- Connect to Exchange Online PowerShell.
- Execute Undo-SoftDeletedMailbox with the mailbox address, the WindowsLiveID and a password.
Undo-SoftDeletedMailbox allieb@contoso.com -WindowsLiveID allieb@contoso.com -Password (Read-Host "Enter password" -AsSecureString)Restore from the same source the user or mailbox was deleted from, Entra ID or Exchange Online. Otherwise the restore fails. Microsoft supplies the command and it is untested here.
How to Preserve a Mailbox for Former Employees?
Place a Litigation Hold on the mailbox before you delete the user. Microsoft calls the result an inactive mailbox. You cannot remove a mailbox under Litigation Hold or eDiscovery hold.
What Happens When You Remove a License?
Removing an Exchange Online license retains the data for 30 days. Add the license again in that period to restore access. Mailboxes without a license are not searchable by Content Search or eDiscovery (Premium).
Related reading: how to merge Outlook archive folders and how to solve a full Outlook mailbox.
Frequently Asked Questions
How Long is a Deleted Mailbox Retained?
30 days in a soft deleted state. After that the mailbox is permanently deleted.
How do I Restore a Deleted Office 365 Mailbox?
Recover the deleted user in the Microsoft 365 admin center or execute Undo-SoftDeletedMailbox in Exchange Online PowerShell.
Can I Restore a Mailbox After 30 Days?
No. Microsoft states a mailbox hard deleted after 30 days cannot be recovered.
Does Microsoft Restore a Mailbox From a Backup?
Microsoft describes soft delete recovery only. It names no backup restore.
Key Takeaways
- Deleted mailboxes remain recoverable for 30 days.
- Restoring the account or executing Undo-SoftDeletedMailbox recovers a mailbox.
- Hard deleted mailboxes cannot be recovered.
- Placing a Litigation Hold before deletion creates an inactive mailbox.
- Removing a license starts the same 30 day period.
Sources and References
Facts follow Microsoft Learn.
- Delete or restore user mailboxes in Exchange Online (Microsoft Learn) learn.microsoft.com