Exchange Online · Mailboxes

Create a shared mailbox in Exchange Online

Written November 12, 2026

Some addresses belong to a team, not a person — info@, frontdesk@, support@. A shared mailbox gives that address a real inbox and calendar that several people open side by side with their own, and replies go out from the shared address. It needs no licence of its own while it stays under 50 GB, and nobody signs in to it directly: members reach it through permissions, which is exactly what this runbook sets up.

What you need

• An account with the Exchange Administrator role (or Global Administrator). Creating mailboxes is an Exchange job, and the pages below simply will not appear without it.
• The address and display name decided. The display name is what recipients see in their inbox list; the address is what they type. Keep both obvious — "Front Desk" and frontdesk@ beats a clever abbreviation nobody guesses.
• The member list. Know who reads and replies from this mailbox before you start. Every member needs their own licensed mailbox; a shared mailbox is not a way to give an unlicensed person email.

Route 1: the admin centre

1. Open the Shared mailboxes page. In the Microsoft 365 admin centre, go to Teams & groups > Shared mailboxes. Use Show all in the left navigation first if the section is collapsed.
2. Add the mailbox. Select Add a shared mailbox, enter the name, and confirm the email address it proposes — you can edit the part before the @. Select Save changes.
3. Add the members. Give it a few minutes to finish provisioning, then under Next steps choose Add members to this mailbox, add the people from your list, and save. Adding someone as a member is what lines up their access — see the permissions section below for what they actually receive.
4. Leave the licence alone. A shared mailbox arrives unlicensed and sign-in to the account is blocked by default. Both are correct. Do not "fix" them by assigning a licence or unblocking sign-in; members never sign in as the mailbox.

Set the delegation properly

Three permissions decide what members can do, and they are not interchangeable:

• Full Access — open the mailbox and work in it as if it were their own: read, reply, delete, manage the shared calendar. With automapping on (the default behaviour when Full Access is granted in the admin tools), the mailbox appears in the member's Outlook on its own.
• Send As — send mail that looks like it came from the shared address itself, not from the member.
• Send on Behalf — send mail that arrives as "member on behalf of the shared address". Use this only when the recipient should see which person wrote back.

Most team mailboxes want Full Access plus Send As for the same group of people. In the admin centre, select the mailbox and use its settings to edit the Send As and Send on Behalf assignments; Full Access is managed from the mailbox's delegation settings in the Exchange admin centre. If you grant Full Access through PowerShell instead, the -AutoMapping flag below decides whether Outlook adds the mailbox automatically.

Route 2: Exchange Online PowerShell

Install the Exchange Online module once (Install-Module ExchangeOnlineManagement -Scope CurrentUser), connect, and the whole job is three commands — create, then grant the two permissions:

Connect-ExchangeOnline

New-Mailbox -Shared `
    -Name "Front Desk" `
    -DisplayName "Front Desk" `
    -Alias frontdesk `
    -PrimarySmtpAddress "frontdesk@contoso.com"

Add-MailboxPermission -Identity "frontdesk@contoso.com" `
    -User "priya@contoso.com" `
    -AccessRights FullAccess `
    -AutoMapping $true

Add-RecipientPermission -Identity "frontdesk@contoso.com" `
    -Trustee "priya@contoso.com" `
    -AccessRights SendAs `
    -Confirm:$false

Repeat the two permission commands for each member, or name a mail-enabled security group as the -User and -Trustee so membership changes later take care of themselves. For Send on Behalf instead of Send As, use Set-Mailbox -Identity "frontdesk@contoso.com" -GrantSendOnBehalfTo "priya@contoso.com".

End state

• The mailbox is listed under Teams & groups > Shared mailboxes with the right address.
• Each member sees the mailbox appear in Outlook (desktop and web) under their own account — allow some time after granting Full Access before calling it broken.
• A test message sent to the shared address lands in the shared inbox, not in a member's personal one.
• A member can reply to it, and the reply goes out from the shared address.

When it goes wrong

• The mailbox never appears in a member's Outlook. Usually Full Access without automapping, or Outlook needing a restart after the permission landed. Check the permission with Get-MailboxPermission -Identity "frontdesk@contoso.com" before changing anything.
• Replies show the member's own address. They have Full Access but not Send As, and Outlook fell back to their account. Grant Send As and have them pick the shared address in the From field once.
• Send As works in Outlook on the web but not the desktop app. The address is often hidden from the address book — Send As and Send on Behalf do not work from the desktop client while the mailbox is hidden from the global address list.
• The mailbox needs archiving or is passing 50 GB. That is when a shared mailbox stops being licence-free: it needs an Exchange Online licence (Plan 2 for in-place archiving and hold features). Assign one rather than deleting mail to stay under the line.