How to Convert a User Mailbox to a Shared Mailbox in Microsoft 365
When an employee leaves an organization, changes roles, or no longer needs an individual email account, IT administrators may need to preserve their mailbox for ongoing business operations. Converting a user mailbox to a shared mailbox in Microsoft 365 allows multiple authorized users to access existing emails, calendar information, and other mailbox content without maintaining it as a regular user’s mailbox.
For organizations using Microsoft 365, this conversion can simplify employee offboarding, reduce unnecessary licensing costs, and ensure business communications remain accessible to the right teams.
In this guide, we’ll explain how to convert a user mailbox to a shared mailbox in Microsoft 365.
Key Takeaways
What is a Shared Mailbox in Microsoft 365?
A shared mailbox in Microsoft 365 refers to an email mailbox that is accessible by multiple users who have been authorized to read, manage emails, and also send emails from the same address. It is unlike the regular user mailboxes, which are meant for individual use.
The use cases may be illustrated by considering the following scenario: In the event a sales employee leaves your company, you may consider changing his or her mailbox to a shared mailbox whereby the sales manager and other authorized personnel can access past emails.
Some of the use cases include:
- Offboarding an Employee: Maintaining business emails after offboarding an employee.
- Internal departmental communication: Managing emails using addresses like support@company.com and sales@company.com.
- Business Continuity: Authorizing employees to reply to customer inquiries.
- Optimization of licenses: Possibly removing the license of the mailbox provided it meets Microsoft shared mailbox criteria.
- Compliance and Retention: Ensuring continued access to mailbox information under license, retention, and compliance policies.
Microsoft confirms that converting a user mailbox to a shared mailbox retains existing email and calendar information.
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Why Convert a User Mailbox to a Shared Mailbox?
Maintaining a separate licensed user account for an employee who no longer needs individual mailbox access may create unnecessary administrative overhead.
Converting the mailbox can help your IT team:
- Retain historical email conversations and calendar information.
- Provide access to managers, department members, or other authorized users.
- Reduce licensing costs when the mailbox qualifies for license removal.
- Simplify employee offboarding and mailbox management.
- Maintain continuity for customer communications and internal workflows.
However, converting a mailbox alone does not complete the offboarding process. Administrators must also secure the former employee’s account, review access permissions, and address retention requirements.
Pre-conversion Prerequisites of User Mailbox
Before beginning the process of conversion, please ensure that the following prerequisites are fulfilled.
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Licensing for the user mailbox must be checked
In Microsoft’s admin-center conversion flow, the requirement is that the user mailbox should have licensing assigned. If you have already removed the license, you might need to assign it again before initiating the conversion process.
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Check mailbox size and licensing needs
An unlicensed shared mailbox normally supports 50GB. However, having an Exchange Online Plan 2 license can make the mailbox support up to 100 GB of mailboxes. In some cases, more licensing will be needed to enable archive storage and other compliance options such as Litigation Hold. Check the licensing terms first before removing the license.
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Determine the list of users
Decide which employees require access to the mailbox, sending emails from it and sending emails as the mailbox.
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Account security check
If the conversion is part of employee offboarding, plan to block the former employee’s sign-in, revoke active sessions where appropriate, and review other access methods. Do not assume that converting the mailbox automatically disables the associated account.
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Do not delete the associated user account
The associated Microsoft 365 user account must remain in place to anchor the shared mailbox. Deleting it can disrupt mailbox access and management.
Method 1: Convert a User Mailbox to a Shared Mailbox Using the Microsoft 365 Admin Center
The Microsoft 365 admin center is a convenient option for administrators who prefer a graphical interface. Follow these steps:
Step 1: Sign in to the Microsoft 365 admin center
Open Microsoft 365 admin center and sign in with an administrator account that has the required permissions.
Step 2: Open Active users
In the navigation menu, go to Users > Active users.
Step 3: Select the user
Find and select the user account whose mailbox you want to convert.
Step 4: Open the Mail tab
In the user’s details pane, select the Mail tab.
Step 5: Select Convert to shared mailbox
Choose Convert to shared mailbox, then select Convert to confirm the operation.
Step 6: Verify the conversion
Allow the change to complete, then check that the mailbox is listed as a shared mailbox and that its existing email and calendar information is available.
Step 7: Review licensing
If the mailbox is eligible to operate without a license, you can remove the license assigned to the former user’s account. Remember that the associated account must remain in place.
These steps follow Microsoft’s documented conversion process. Read Microsoft’s official guide.
Method 2: Convert a User Mailbox to a Shared Mailbox Using the Exchange Admin Center
Exchange administrators can also perform the conversion through the Exchange admin center (EAC).
Follow these steps:
Step 1: Open the Exchange admin center
Go to Exchange admin center and sign in with an account that has the necessary Exchange permissions.
Step 2: Navigate to Mailboxes
Select Recipients > Mailboxes.
Step 3: Select the user mailbox
Locate the mailbox you want to convert and select it.
Step 4: Choose the conversion option
In the available actions, select Convert to shared mailbox. Depending on the interface, this may appear in the More actions pane.
Step 5: Confirm the conversion
Review the selected mailbox and confirm the operation.
Step 6: Verify the mailbox type
Confirm that the conversion completed successfully and that the mailbox is now identified as a shared mailbox.
The Exchange admin center is particularly useful for administrators who manage mailbox recipients and permissions directly. Microsoft estimates that the conversion procedure takes approximately five minutes, although administrative processing and verification can take additional time.
Method 3: Convert a User Mailbox to a Shared Mailbox Using PowerShell
For IT administrators managing multiple mailboxes or automating administrative tasks, Exchange Online PowerShell provides a command-line alternative.
Step 1: Connect to Exchange Online PowerShell
Install the Exchange Online PowerShell module if it is not already installed:
Install-Module ExchangeOnlineManagement
Then connect to Exchange Online:
Connect-ExchangeOnline
Sign in using an account with the required Exchange permissions.
Step 2: Identify the mailbox
Before making changes, verify the mailbox identity and its current type:
Get-Mailbox -Identity “user@company.com” |
Format-List DisplayName,PrimarySmtpAddress,RecipientTypeDetails
Replace user@company.com with the actual mailbox address.
Step 3: Convert the mailbox
Run the following command:
Set-Mailbox -Identity “user@company.com” -Type Shared
This changes the mailbox type from a regular user mailbox to a shared mailbox.
Step 4: Verify the conversion
Run the verification command:
Get-Mailbox -Identity “user@company.com” |
Format-List DisplayName,PrimarySmtpAddress,RecipientTypeDetails
Check that RecipientTypeDetails returns SharedMailbox.
Step 5: Disconnect the session
After completing the operation, disconnect from Exchange Online:
Disconnect-ExchangeOnline -Confirm:$false
Important: In hybrid Exchange environments, mailbox management may need to be performed using on-premises Exchange tools, including the appropriate remote mailbox commands. Confirm your environment’s configuration before running conversion commands. For more information, refer to Microsoft’s Exchange Online mailbox conversion documentation.
Access Permission Configuration for the Shared Mailbox
Despite turning the mailbox into a shared one, all employees do not automatically get access permissions. It is necessary to set up these permissions.
These include the following two types of access permission:
Full Access (Read and Manage): This gives the person access to the shared mailbox, where he/she can read emails and create or modify mailbox items.
Send As: This permits sending emails from the shared mailbox on behalf of the person.
The third kind of access permission is “Send on Behalf.” It allows sending emails on behalf of the mailbox, and the identity of the person is visible to the recipient.
Delegation of a mailbox can be done through the following steps:
- Exchange admin center should be opened.
- Recipients -> Mailboxes should be selected.
- The shared mailbox should be selected.
- Mailbox delegation should be opened.
- Users should be added for full access, “Send As” and “Send on Behalf” of the shared mailbox.
- The configuration should be saved and verified.
Only those permissions which are required by the users should be assigned to them.
Can You Remove the Microsoft 365 License After Conversion?
Yes, in many cases. An eligible shared mailbox can operate without an assigned license when its requirements are met.
Before removing the license, check these conditions:
- The mailbox is no larger than 50 GB.
- The mailbox does not require a license-dependent archive or compliance feature.
- The applicable retention and legal requirements are satisfied.
- The associated user account remains in place.
If the mailbox exceeds 50 GB, an appropriate license is required. Exchange Online Plan 2 supports a mailbox of up to 100 GB, while additional licensing may be required for archive expansion or certain hold features.
Important: Removing a license is not the same as deleting a user account. Complete the conversion first, verify mailbox access, and only then make licensing changes.
Common Problems with Conversion of User Mailbox into Shared Mailbox
Despite the simplicity of the process, there are still some common problems that may arise.
1. The ‘Convert to shared mailbox’ option is missing
Cause: No license for the user mailbox or lack of permission.
Resolution: Check license assignment and administrator rights and make sure everything is correct; if it’s not, assign the license and repeat the process.
2. The shared mailbox is not showing in Outlook
Cause: The mailbox permissions have not propagated, or the Outlook profile has not been updated.
Resolution: Make sure the permissions are set correctly; restart the application if necessary. If the automatic mapping is not available, add the shared mailbox manually.
3. Users can access the mailbox but cannot send emails
Cause: Only full access permission was granted but the ‘send as’ or ‘send on behalf’ is missing.
Resolution: Give the corresponding permission and wait for the changes to propagate.
4. The mailbox becomes inaccessible after the license is removed
Cause: The mailbox is over the unlicensed size limit or uses a licensed feature.
Resolution: Ensure mailbox size, archiving needs, holds, and licensing requirements have been considered before removing or reassigning the license.
5. Shared mailbox changes to user mailbox in hybrid deployments
Cause: Attributes of on-premises Exchange Server and directory synchronization may affect mailbox classification.
Resolution: Check the hybrid setup and manage remote mailbox from on-premises Exchange Server. Synchronization ensures recipient type is set as expected.
Best practices for converting mailboxes while offboarding an employee
Mailbox conversion must be a step in an offboarding process designed by IT team in the enterprise organization.
- Protect the account: Prevent sign-ins and terminate sessions as necessary to prevent any misuse.
- Ensure continuity of business: Verify that email, calendar data, retention policy, and required archives are accessible.
- Control access: Provide mailbox permission to authorized personnel only.
- Review licensing: Remove unnecessary licenses only after verifying that the mailbox meets all requirements.
- Document the changes: Record the mailbox type, permission assignments, license changes, and relevant approvals.
- Test business continuity: Verify that the intended users can access the mailbox and send messages correctly.
- Account for hybrid dependencies: Check whether on-premises Exchange management or directory synchronization affects the conversion.
These steps help reduce disruption and maintain control over business communications.
Convert a User Mailbox to a Shared Mailbox in Microsoft 365 Today!
Converting a user mailbox to a shared mailbox in Microsoft 365 is a practical way to preserve business communications, support employee offboarding, and simplify mailbox management. Administrators can complete the process through the Microsoft 365 admin center, Exchange admin center, or Exchange Online PowerShell.
Frequently Asked Questions
1. Is there going to be any loss of existing emails during conversion of a user mailbox into a shared mailbox?
No. The process of conversion performed by Microsoft will keep existing emails and calendar entries. However, access and retention policies should be checked post-conversion.
2. Can I revert a shared mailbox back into a user mailbox?
Yes. It can be reverted back using Exchange admin center and requires an adequate user license to be assigned.
3. Can I convert a mailbox without any licenses?
The Microsoft 365 admin center process requires that the user mailbox have an adequate license before you can perform the conversion. Post-conversion, the shared mailbox will not require a license anymore.
4. Does a shared mailbox require a different password?
Access to a shared mailbox is usually done using an authorized user account and not by logging in as a shared mailbox user account directly, which should be restricted.
5. Can more than one user use the same shared mailbox?
Yes. Administrators can give permission and assign necessary access to more than one user in a shared mailbox.
6. Is PowerShell better than the admin center?
It depends on the task. The admin center is suitable for individual mailbox conversions. However, PowerShell is useful for repeatable administrative tasks, scripting, and managing larger environments.
About the Author: Aayushi Raj
