Create and manage inactive mailboxes
Microsoft 365 makes it possible for you to retain the contents of deleted mailboxes. This feature is called inactive mailboxes. Inactive mailboxes allow you to retain former employees' email after they leave your organization. A mailbox becomes inactive when a Litigation Hold or a retention policy (created in the security and compliance center in Office 365 or Microsoft 365) is applied to the mailbox before the corresponding user account is deleted. The contents of an inactive mailbox are retained for the duration of the hold that was placed on the mailbox before it was made inactive. This allows administrators, compliance officers, and records managers to use Content Search to search and export the contents of an inactive mailbox. Inactive mailboxes can't receive email and aren't displayed in your organization's shared address book or other lists.
As we continue to invest in different ways to preserve mailbox content, we're announcing the retirement of In-Place Holds in the Exchange admin center. That means you should use Litigation Holds and retention policies to create an inactive mailbox. Starting July 1, 2020 you won't be able to create new In-Place Holds in Exchange Online. But you'll still be able to change the hold duration of an In-Place Hold placed on an inactive mailbox. However, starting October 1, 2020, you won't be able to change the hold duration. You'll only be able to delete an inactive mailbox by removing the In-Place Hold. Existing inactive mailboxes that are on In-Place Hold will still be preserved until the hold is removed. For more information about the retirement of In-Place Holds, see Retirement of legacy eDiscovery tools.
Preparations before creating an inactive mailbox
To make a mailbox inactive, it must be assigned an Exchange Online Plan 2 license so that a Litigation Hold or a retention policy can be applied to the mailbox before it's deleted. Exchange Online Plan 2 licenses are part of an Office 365 Enterprise E3 and E5 subscription. If a mailbox is assigned an Exchange Online Plan 1 or Exchange Online Kiosk license (which are part of an Office 365 E1 and F1 subscription respectively), you would have to assign it a separate Exchange Online Archiving license so that a hold can be applied to the mailbox before it's deleted. For more information, see Exchange Online Archiving.
The licenses associated with the deleted Exchange Online mailbox will be available after you delete the corresponding user account. You can then assign those licenses to another user.
If a Litigation Hold or a retention policy (that's configured to retain or retain and then delete content) isn't applied to a mailbox before it's deleted, the contents of the mailbox won't be retained or discoverable. However, the deleted mailbox can be recovered within 30 days of deletion, but the mailbox and its contents will be permanently deleted after 30 days if it isn't recovered.
For more information about Litigation Hold, see Litigation Hold. For more information about retention policies, see Learn about retention policies and retention labels.
Create an inactive mailbox
Making a mailbox inactive involves two steps: 1) placing the mailbox on Litigation Hold or applying a retention policy to it, and 2) deleting the mailbox or corresponding user account. After the mailbox is inactive, its contents are retained until the hold or retention policy is removed.
Step 1: Place a mailbox on Litigation Hold or apply a retention policy
Placing a mailbox on Litigation Hold or applying a retention policy (that's configured to retain or retain and then delete content) retains the contents in the mailbox before it's deleted. Both types of holds will retain all mailbox content, including deleted items and original versions of modified items. Deleted and modified items are retained in the inactive mailbox for a specified period, or until you permanently delete the inactive mailbox by removing the hold or retention policy that's applied to the inactive mailbox.
If a hold is already placed on a mailbox, or if a retention policy is already applied to a mailbox, then all you have to do is delete the corresponding user account as explained in Step 2.
For step-by-step procedures for placing a mailbox on Litigation Hold or applying a retention policy, see:
For Litigation Holds and retention policies, you can create an indefinite hold or on a time-based hold. In an indefinite hold, the contents of the inactive mailbox will be retained forever, or until the hold is removed or until the hold duration is changed. After the hold or retention policy is removed (assuming that the mailbox was deleted more than 183 days ago), the inactive mailbox will be marked for permanent deletion and the contents of the mailbox will no longer be retained or discoverable. In a time-based hold or retention policy, you specify the duration of the hold. This duration is on a per-item basis and is calculated from the date a mailbox item was received or created. After the hold expires for a mailbox item, and that item moved to or is located in the Recoverable Items folder in the inactive mailbox, the item is permanently deleted (purged) from the inactive mailbox after the deleted item retention period expires.
Step 2: Delete the mailbox
After the mailbox is placed on hold or a retention policy is applied to it, the next step is to delete the mailbox. The best way to delete a mailbox is to delete the corresponding user account in the Microsoft 365 admin center. For information about deleting user accounts, see Delete a user from your organization.
You can also delete the mailbox by using the Remove-Mailbox cmdlet in Exchange Online PowerShell. For more information, see Delete or restore user mailboxes in Exchange Online.
View a list of inactive mailboxes
To view a list of the inactive mailboxes in your organization:
Go to https://compliance.microsoft.com and sign in using the credentials for an Global administrator or a Compliance administrator account in your organization.
In the left navigation pane of the Microsoft 365 compliance center, click Show all, and then click Information governance > Retention.
On the Retention page, click Inactive mailbox to display a list of inactive mailboxes.
Select an inactive mailbox to display a flyout page with information about the inactive mailbox.
You can click Export to view or download a CSV file that contains additional information about the inactive mailboxes in your organization.
Alternatively, you can run the following command in Exchange Online PowerShell to display the list of inactive mailboxes.
Get-Mailbox -InactiveMailboxOnly | FT DisplayName,PrimarySMTPAddress,WhenSoftDeleted
You can also run the following command to export the list of inactive mailboxes and other information to a CSV file. In this example, the CSV file is created in the current directory.
Get-Mailbox -InactiveMailboxOnly | Select Displayname,PrimarySMTPAddress,DistinguishedName,ExchangeGuid,WhenSoftDeleted | Export-Csv InactiveMailboxes.csv -NoType
It's possible that an inactive mailbox may have the same SMTP address as an active user mailbox. In this case, the value of the DistinguishedName or ExchangeGuid property can be used to uniquely identify an inactive mailbox.
Search and export the contents of an inactive mailbox
You can access the contents of the inactive mailbox by using the Content Search tool in the Security & Compliance Center. When you search an inactive mailbox, you can create a keyword search query to search for specific items or you can return the entire contents of the inactive mailbox. You can preview the search results or export the search results to an Outlook Data (PST) file or as individual email messages. For step-by-step procedures for searching mailboxes and exporting search results, see the following topics:
Here are a few things to keep in mind when searching inactive mailboxes.
If a content search includes a user mailbox and that mailbox is made inactive, the content search will continue to search the inactive mailbox when you rerun the search after it becomes inactive.
In some cases, a user may have an active mailbox and an inactive mailbox that have the same SMTP address. In this case, only the specific mailbox that you select as a location for a content search will be searched. In other words, if you add a user's mailbox to a search, you can't assume that both their active and inactive mailboxes will be searched; only the mailbox that you explicitly add to the search will be searched.
We strongly recommend that you avoid having an active mailbox and inactive mailbox with the same SMTP address. If you need to reuse the SMTP address that is currently assigned to an inactive mailbox, we recommend that you recover the inactive mailbox or restore the contents of an inactive mailbox to an active mailbox (or the archive of an active mailbox), and then delete the inactive mailbox.
Change the hold duration for an inactive mailbox
After a mailbox is made inactive, you can change the duration of the hold or the retention policy applied to the inactive mailbox. For step-by-step procedures, see Change the hold duration for an inactive mailbox in Office 365.
Recover an inactive mailbox
If a former employee returns to your organization, or if a new employee is hired to take on the job responsibilities of the departed employee, you can recover the contents of the inactive mailbox. When you recover an inactive mailbox, the mailbox is converted to a new mailbox, the contents and folder structure of the inactive mailbox are retained, and the mailbox is linked to a new user account. After it's recovered, the inactive mailbox no longer exists. For step-by-step procedures and more information about happens when you recover an inactive mailbox, see Recover an inactive mailbox in Office 365.
Restore the contents of an inactive mailbox to another mailbox
If another employee takes on the job responsibilities of a former employee, or if another person needs access to the contents of the inactive mailbox, you can restore (or merge) the contents of the inactive mailbox to an existing mailbox. When you restore an inactive mailbox, the contents are copied to another mailbox. The inactive mailbox is retained and remains an inactive mailbox. The inactive mailbox can still be searched using eDiscovery, its contents can be restored to another mailbox, or it can be recovered or deleted at a later date. For step-by-step procedures, see Restore an inactive mailbox in Office 365.
Delete an inactive mailbox
If you no longer need to retain the contents of an inactive mailbox, you can permanently delete the inactive mailbox by removing the hold or removing the retention policy applied to the inactive mailbox. The mailbox will be retained for 183 days after you remove the hold or retention policy. After 183 days, the mailbox will be marked for permanent deletion, and the mailbox will become non-recoverable. If the inactive mailbox was deleted within the last 183 days, you can still recover it. For step-by-step procedures for removing a hold or a retention policy to permanently delete an inactive mailbox, see Delete an inactive mailbox.