Convert user mailbox to shared mailbox and shared mailbox licensing

Convert a mailbox without losing its email or calendar, then check access and licensing.

Who this is for: Microsoft 365 administrators managing Exchange Online user and shared mailboxes.

Use this guide when a mailbox needs to be shared by several people instead of being used by one person. The conversion retains existing email and calendar information, but the mailbox’s licence needs may change. These steps cover Exchange Online in a cloud-only environment; hybrid Exchange environments have a separate management process.

Before you start

Make sure a licence is assigned to the user mailbox before conversion. If it is not licensed, the option to convert it will not appear.
Do not delete the user account associated with the mailbox. The account is needed to anchor the shared mailbox.
Check the mailbox size and whether it uses archiving, a hold, or other advanced features. These can affect whether you can remove its licence.
Plan who needs access. A shared mailbox supports up to 25 users; use a Microsoft 365 group instead if more than 25 people need access. People using a shared mailbox need their own licensed Exchange Online mailbox, and access is for people inside your organisation.
Keep sign-in blocked for the shared mailbox account. A shared mailbox is not intended for direct sign-in.

In the Microsoft 365 admin center, block sign-in for the associated user account. For blocking instructions, see [Create a shared mailbox](https://learn.microsoft.com/en-us/microsoft-365/admin/email/create-a-shared-mailbox), which links to instructions for blocking Microsoft 365 user accounts.
Check the account’s sign-in status in the admin center and confirm that it is blocked.

Important If your organisation uses Exchange hybrid, do not rely on these cloud-only conversion steps. Microsoft directs hybrid administrators to the on-premises Exchange process for managing shared mailboxes.

Convert the user mailbox

Sign in to the Microsoft 365 admin center.
Open Users > Active users.
Select the user whose mailbox you want to convert.
Open the Mail tab.
Select Convert to shared mailbox.
Select Convert to confirm.

Note You do not need to reset the user’s password just to convert the mailbox. However, if you do not reset it, the original username and password continue to work on the mailbox after conversion. Keep sign-in blocked for the shared mailbox account; if the mailbox belongs to a departing employee, take the additional steps needed to prevent that person from signing in.

Give people access

Converting the mailbox does not replace the need to give the right people access. Shared mailboxes are for internal users, and each person who uses one needs a licensed Exchange Online mailbox of their own. The shared mailbox does not need a separate licence for basic use within the limits described below.

In the Microsoft 365 admin center, open Teams & groups > Shared mailboxes.
Select the converted mailbox.
Select Edit under Members.
Select Add members.
Choose the people who need access.
Select Save.

Check the licensing before removing a licence

Important Before deleting messages to reduce the mailbox size, confirm they are no longer needed and check applicable retention or hold requirements. Deleting messages removes mailbox content. If you need to retain the content, keep an appropriate licence instead.

An unlicensed shared mailbox can store up to 50 GB. You can remove the licence from the user’s account after conversion only when the mailbox is smaller than 50 GB and its other requirements do not call for a licence. If the mailbox is too large, you might need to remove large messages, such as messages with attachments, before you can remove the licence.

For a shared mailbox that needs a storage limit of up to 100 GB, assign it an Exchange Online Plan 2 licence.
To increase archive mailbox storage, use Exchange Online Plan 2 or Exchange Online Plan 1 with an Exchange Online Archiving add-on licence. Either option also lets you enable auto-expanding archiving.
A shared mailbox on an In-Place Hold or Litigation Hold needs Exchange Online Plan 2, or Exchange Online Plan 1 with an Exchange Online Archiving add-on licence.
Advanced features, including Microsoft Defender for Office 365, Microsoft Purview eDiscovery (Premium), and retention policies, might require licences.

Check it worked

Confirm that the mailbox appears on the Shared mailboxes page and that the intended people are listed as members.
Confirm that the original email and calendar information is present. Conversion retains this information, and inbox rules are preserved.
Confirm the associated user account still exists and that sign-in is blocked.
Before removing a licence, confirm the mailbox is smaller than 50 GB and check for archiving, hold, or advanced-feature requirements.

When it goes wrong

Symptom	Likely cause	Fix
Convert to shared mailbox is not available.	The user mailbox does not have a licence assigned.	Assign a licence to the user mailbox, then return to Users > Active users and try the conversion again.
You cannot remove the licence without reducing the mailbox size.	The mailbox is not smaller than 50 GB, which is the unlicensed shared mailbox limit.	Keep an appropriate licence, or reduce the mailbox size by deleting large messages only after confirming they are no longer needed and checking applicable retention or hold requirements. Exchange Online Plan 2 supports a shared mailbox size limit of up to 100 GB.
A person cannot access the shared mailbox.	They may not be a member, or may not have their own licensed Exchange Online mailbox.	Add the person under Members and check that they have a licensed Exchange Online mailbox.
The old username and password still work.	The original credentials can continue to work after conversion if the password was not reset.	Keep sign-in blocked for the shared mailbox account. Do not use that account to sign in to the mailbox.

Last updated on October 13, 2026