How to restore a deleted mailbox in Office 365

How Exchange Online deletes mailboxes

Exchange Online treats a deleted mailbox in one of three ways, and the right fix depends on which one applies. Microsoft's own documentation describes them:

Microsoft notes that it "strongly recommend[s] restoring the mailbox from the same source (Microsoft Entra ID or Exchange Online) from where the user or mailbox was deleted"; mixing the two can make the restore fail. The Microsoft 365 admin centre also offers an automated diagnostic that reports the current state of a recently deleted mailbox, which is a good first check.

Restore a deleted user mailbox in the admin centre

If the mailbox disappeared because the user account was deleted, restoring the user restores the mailbox with it.

1. Sign in to the Microsoft 365 admin centre with an account that can manage users
2. Go to Users then Deleted users. Users deleted in the last 30 days are listed here
3. Select the user and choose Restore user, then set how the password should be handled
4. Check the restored account has a licence that includes Exchange Online, so the mailbox becomes active again
5. Wait for the change to replicate, then confirm that mail, calendar and contacts are present in Outlook on the web

If the user is not listed, more than 30 days have passed or the account was permanently removed, and the admin centre cannot help. Go to the backup section below.

Restore a soft-deleted mailbox with PowerShell

Exchange Online PowerShell gives more control and is the usual route when the admin centre is not enough:

1. Connect to Exchange Online PowerShell with an account that has recipient management permissions
2. List soft-deleted mailboxes with Get-Mailbox -SoftDeletedMailbox and note the name and ExchangeGuid of the one you need
3. Run Undo-SoftDeletedMailbox, giving the mailbox and its sign-in address; you are prompted to set a password
4. In a hybrid deployment where the Microsoft Entra user has been hard-deleted, create a target mailbox and use New-MailboxRestoreRequest, with the soft-deleted mailbox's GUID as the source, to copy the content into it
5. Check progress with Get-MailboxRestoreRequest and Get-MailboxRestoreRequestStatistics until the request completes

New-MailboxRestoreRequest is also useful when you want the old content in a different mailbox, for example a manager's, rather than bringing the leaver's account back to life.

Licence removed, shared mailboxes and deleted items

Licence removed by mistake When an Exchange Online licence is removed, Microsoft holds the mailbox data for 30 days. Assign the licence again within that grace period and the mailbox becomes fully active. After 30 days the data is deleted and cannot be recovered. A de-licensed mailbox also cannot be searched with Microsoft Purview eDiscovery, which matters if you are responding to a legal request.

Shared mailboxes Every shared mailbox has a corresponding user account in Microsoft 365, so a deleted shared mailbox is handled through that account: check Deleted users and the list from Get-Mailbox -SoftDeletedMailbox within the same 30-day window. Shared mailboxes are often missed by backups, so check yours covers them: Microsoft 365 Backup covers user and shared mailboxes, and the platforms we supply list shared mailboxes too. See Exchange Online backup for what each product includes.

A few deleted emails, not the whole mailbox If the mailbox still exists and only some messages are missing, users can use Recover deleted items in Outlook. Exchange Online keeps deleted items for 14 days by default, which an admin can raise to 30. The Microsoft 365 recycle bin page covers these limits.

After 30 days: inactive mailboxes and backups

Once the 30 days have passed, there are only two ways back.

Inactive mailboxes. If a Litigation Hold, eDiscovery hold or retention policy covered the mailbox before the user was deleted, Exchange Online keeps it as an inactive mailbox. The content is preserved for compliance and can be searched and recovered, but this must be set up before the deletion, and holds on shared mailboxes need an Exchange Online Plan 2 licence or Exchange Online Archiving. Our sister site covers leavers' mailboxes and legal hold in detail.

A backup. A third-party backup keeps its own copy outside Microsoft 365, so it is not affected when the user, licence or mailbox is removed. Depending on the product and how retention is set, you can restore the whole mailbox into a new or existing mailbox, restore individual folders or items, or export to PST. Axcient says x360Cloud keeps data for departed users, and other platforms let you choose how long leavers' backups are kept; Microsoft says Microsoft 365 Backup keeps the backups of removed or deleted users for one year from creation. Check this setting before you rely on it, because it decides whether old mail is still there when someone asks for it.

Many organisations convert a leaver's mailbox to a shared mailbox (up to 50 GB without a licence) or keep it on hold. A backup does not replace either, but it does protect against the mistake of deleting the account before anyone has checked what was in it.

Before you delete a mailbox: a short checklist

Many mailbox restore requests can be avoided by a few minutes' checking before the account is removed:

1. Decide what should happen to the mailbox: convert it to a shared mailbox, place it on hold so it becomes inactive, export it, or let it be deleted
2. If anyone needs ongoing access, grant it before deletion, and set up forwarding or an auto-reply if customers still write to the address
3. Check whether the mailbox has an archive mailbox, and whether your backup covers archive mailboxes (Acronis lists them as an option and Commvault includes them in its Enterprise editions; check the others)
4. Confirm the mailbox appears in your backup and note how long the backup keeps leavers' data
5. Remember that removing the licence starts a 30-day clock just as deleting the user does
6. Record the date you deleted the account, so you know which recovery route is still open if someone asks later

Group mailboxes belong to Microsoft 365 groups and follow the group's 30-day soft-delete period rather than the user rules above. Microsoft 365 Backup does not cover group or room mailboxes, so if those matter to you, choose a product that lists them; Acronis and Commvault both include group mailboxes.

How we help

We can check which of your mailboxes are protected today, including shared, group and archive mailboxes, and set up a leaver process that keeps what you need without paying for licences you do not need. If you choose a backup, we can connect it, set leaver retention to suit you and run a test mailbox restore with you before handover. Pricing depends on users, mailboxes and retention, so ask us for a quote.

Contact us about protecting your mailboxes.