How to Create a Shared Mailbox in Microsoft 365 –

A shared mailbox lets a team read and send mail from one common address (for example, support@contoso.com) without anyone needing its password. Replies sent from it show the shared address, not the individual’s. Each shared mailbox also comes with a shared calendar. Source: Create a shared mailbox.

Use a Microsoft 365 group instead if you need external members, more than 25 users, or control over deletion. A shared mailbox can’t later be migrated into a group. Source: About shared mailboxes.

Prerequisites

You need an account with the Exchange Administrator (or Global Administrator) role and a Microsoft 365 business plan that includes Exchange Online email. Microsoft 365 Apps for business does not include email, so it can’t host a shared mailbox.

Have these ready before you start:

• Display name for the mailbox (e.g. “Customer Support”)
• Email address and domain (e.g. support@contoso.com)
• List of users who need access, and whether each needs Full Access, Send As, or Send on Behalf
• Confirmation every member has their own licensed Exchange Online mailbox

Hybrid environments: if your organization runs hybrid Exchange, create and manage shared mailboxes in the on-premises Exchange admin center instead of the steps below.

Method 1: Microsoft 365 admin center (recommended)

This is the quickest route for a single mailbox and takes about 10 minutes.

1. Sign in to the Microsoft 365 admin center with an Exchange admin account.
2. Go to Teams & groups > Shared mailboxes. If Teams & groups isn’t visible, select Show all in the left pane.
3. Select + Add a shared mailbox.
4. Enter the Name. The email address fills in from it; edit the alias or domain if needed.
5. Select Save changes. Wait a few minutes before adding members.
6. Under Next steps, select Add members to this mailbox, then Add members.
7. Pick the users who should use the mailbox, select Add, then Close. Members get Full Access and Send As.

Then secure the mailbox’s account:

1. Go to Users > Active users and find the shared mailbox account (filter by Unlicensed users if needed).
2. Select it and choose Block sign-in. If it shows “Sign in blocked,” it’s already done.
3. Tick Block this user from signing in and select Save changes.

Every shared mailbox has a hidden user account with a system-generated password. Blocking sign-in stops anyone who resets that password from logging in to it directly. New shared mailboxes are normally created with sign-in blocked; check it anyway.

If the account has a license you don’t need (for example, after converting a user mailbox), remove it under Users > Active users > [mailbox] > Licenses and apps, then Save changes. Remove the license from your subscription too, or you keep paying for it.

Method 2: Exchange admin center (EAC)

Use the EAC if you prefer to set permissions in the same place you create the mailbox. Source: Shared mailboxes in Exchange Online.

1. Open the Exchange admin center and sign in as an Exchange admin.
2. Go to Recipients > Mailboxes and select Add a shared mailbox.
3. Fill in Display name, Email address, and Alias.
4. Select Create.
5. Under Next steps, select Add users to this mailbox.
6. Select Add users, choose the people who need access, and select Save. This grants Full Access and Send As.
7. Block sign-in for the mailbox’s account in the Microsoft 365 admin center, as in Method 1.

Method 3: Exchange Online PowerShell

Use PowerShell for bulk creation, scripting, or settings the portals don’t expose (such as Send on Behalf or turning off automapping). Replace the example names and addresses with your own.

1. Install the module (once) and connect:

Install-Module ExchangeOnlineManagement -Scope CurrentUser
Connect-ExchangeOnline -UserPrincipalName admin@contoso.com

2. Create the shared mailbox:

New-Mailbox -Shared -Name "Customer Support" -DisplayName "Customer Support" -Alias support -PrimarySmtpAddress support@contoso.com

3. Grant a user Full Access and Send As:

Add-MailboxPermission -Identity support@contoso.com -User jane@contoso.com -AccessRights FullAccess -InheritanceType All
Add-RecipientPermission -Identity support@contoso.com -Trustee jane@contoso.com -AccessRights SendAs -Confirm:$false

4. Confirm it was created:

Get-Mailbox support@contoso.com | Format-List DisplayName,PrimarySmtpAddress,RecipientTypeDetails

RecipientTypeDetails should read SharedMailbox. Microsoft’s own one-line example, which grants a mail-enabled security group Full Access and Send on Behalf, is in Shared mailboxes in Exchange Online. Granting access through a group disables automapping, so the mailbox won’t appear in members’ Outlook on its own.

Assign permissions

Most teams need Full Access plus Send As. Full Access alone lets someone read and manage mail but not send from the mailbox.

To change permissions later in the EAC: Recipients > Mailboxes > select the mailbox > Manage mailbox delegation, then Edit next to the permission type.

Send on Behalf example:

Set-Mailbox support@contoso.com -GrantSendOnBehalfTo @{Add="jane@contoso.com"}

Keep the mailbox visible in the global address list. Send As and Send on Behalf don’t work in Outlook desktop if the mailbox is hidden from address lists.

How users open the mailbox

Users sign in with their own account; they never use a password for the shared mailbox.

Microsoft’s user guides: Outlook for Windows, Outlook on the web, Outlook mobile. Menu names shift between Outlook versions; check these if a step doesn’t match.

Troubleshooting and FAQ

Can I convert an existing user’s mailbox instead? Yes: Users > Active users > select the user > Mail > Convert to shared mailbox. Convert before removing the license, or the mailbox is deleted 30 days after unlicensing.

Can external users get access? No. Use a Microsoft 365 group for that.