# Microsoft 365 shared mailbox vs distribution group vs Microsoft 365 Group

Source: https://srvscripts.com/guides/shared-mailbox-vs-distribution-group/
Updated: 2026-10-06
Publisher: srvScripts (https://srvscripts.com/)

In short: Use a shared mailbox when a team needs a common inbox with shared read state, a sent-items folder and no licence up to 50 GB.

Every organisation eventually needs an address such as support@ or sales@ that several people handle. Microsoft 365 offers three objects that can answer it, and picking the wrong one leads to lost messages, licensing surprises or a Teams team nobody asked for. The three are not interchangeable: a shared mailbox stores mail in one place that several people open, a distribution group copies each message into every member’s own mailbox, and a Microsoft 365 Group is a collaboration bundle with a mailbox, a SharePoint site, a calendar and optionally a Teams team attached. This guide sets out when each one fits and how to create or convert them.

**Short answer:** Use a shared mailbox when a team needs a common inbox with shared read state, a sent-items folder and no licence up to 50 GB. Use a distribution group when the goal is simply to fan a message out to a list of people who each handle it in their own mailbox. Use a Microsoft 365 Group when the team also needs shared files, a calendar and possibly Teams, and accept that its mailbox behaves like a conversation archive rather than an inbox. Shared mailboxes and distribution groups can be converted; Microsoft 365 Groups cannot be converted back.

## Shared mailbox

A shared mailbox is a real Exchange Online mailbox without its own login. Members receive Full Access and usually Send As or Send on Behalf, and it appears as a second mailbox in Outlook and on mobile. Because everyone sees the same read and unread state and the same folders, it suits a support queue or a finance inbox where handling must be visible to colleagues. It needs no licence while under 50 GB and without an archive or litigation hold; beyond that it must be assigned an Exchange Online plan. Create and delegate one with Exchange Online PowerShell:

```
Connect-ExchangeOnline
New-Mailbox -Shared -Name "Support" -DisplayName "Support" -PrimarySmtpAddress support@example.com
Add-MailboxPermission -Identity support@example.com -User alice@example.com -AccessRights FullAccess -AutoMapping $true
Add-RecipientPermission -Identity support@example.com -Trustee alice@example.com -AccessRights SendAs -Confirm:$false
Set-Mailbox -Identity support@example.com -MessageCopyForSentAsEnabled $true -MessageCopyForSendOnBehalfEnabled $true
```

The last line keeps a copy of replies in the shared mailbox’s Sent Items, which is off by default and a frequent complaint. The shared mailbox has no password and sign-in should stay blocked; if someone needs to log in directly, that is a sign a licensed user mailbox is the right object.

## Distribution group

A distribution group is a list. Mail to sales@ is delivered to each member’s inbox with no central copy, no shared state and no shared Sent Items. That suits announcements, on-call rotations and small teams who each own what they pick up, and it is the lightest object to manage. It can be restricted to internal senders, moderated, and nested inside other groups:

```
New-DistributionGroup -Name "Sales Team" -PrimarySmtpAddress sales@example.com -Members alice@example.com,bob@example.com
Set-DistributionGroup -Identity sales@example.com -RequireSenderAuthenticationEnabled $false
Get-DistributionGroupMember -Identity sales@example.com
```

Set `RequireSenderAuthenticationEnabled` to false only for addresses that must accept external mail. Groups cannot be given Send As by default, but a member can be granted it so replies come from the group address. Dynamic distribution groups build membership from attributes such as department, which suits large organisations with reliable directory data.

## Microsoft 365 Group

A Microsoft 365 Group creates a group mailbox, a SharePoint document library, a shared calendar, a Planner plan and, if you choose, a Teams team, all with one membership list. Members see conversations in Outlook’s Groups section or in Teams rather than in their inbox unless they subscribe, and there is no shared read state or per-message ownership. It is the right choice for a project team that needs files and chat with the address as a side effect, and the wrong choice for a support inbox. Creating one from the Microsoft 365 admin center or with `New-UnifiedGroup` produces all the components at once; expect users to ask where the SharePoint site came from.

## Choosing and converting

Ask two questions. Does the team need to see whether a colleague already replied? If yes, a shared mailbox. Do they need shared files, a calendar and Teams tied to the same membership? If yes, a Microsoft 365 Group. Otherwise, a distribution group. Existing objects can be reshaped to a point: `Set-Mailbox -Type Shared` converts a licensed user mailbox to a shared one and back with `-Type Regular`, and a distribution group can be upgraded to a Microsoft 365 Group from the admin center when it has no nested groups and no on-premises sync. A Microsoft 365 Group cannot be downgraded, so treat that upgrade as one-way.

## Verify and keep it tidy

After creating any of the three, send a test message from an external address and confirm delivery lands where expected, then reply and confirm the From address and the Sent Items copy. Check `Get-Mailbox support@example.com | Format-List RecipientTypeDetails, ProhibitSendReceiveQuota` for the shared mailbox type and quota. The common pitfall is a shared mailbox that grows past 50 GB unnoticed and stops receiving mail; set a retention policy or assign a licence before that happens. For the leaver side of these objects see [Offboarding an employee: checklist for Active Directory, Microsoft 365, Google Workspace and Zoho](/guides/employee-offboarding-checklist/).

## Shared mailbox vs distribution group at a glance

**Official documentation:** [Microsoft 365 documentation](https://learn.microsoft.com/en-us/microsoft-365/), [RFC 5321 (SMTP)](https://www.rfc-editor.org/rfc/rfc5321).

**Related guides:** [Microsoft 365: set up SPF, DKIM and DMARC for Exchange Online](https://srvscripts.com/guides/microsoft-365-spf-dkim-dmarc-exchange-online/) · [Exim 4.99/4.100 on cPanel and DirectAdmin: the 2026 security fixes and what changed for admins](https://srvscripts.com/guides/exim-4-100-security-fixes/) · [Roundcube “database error” and webmail login loops on cPanel](https://srvscripts.com/guides/roundcube-database-error-login-loop/).

## Frequently asked questions

### Does a shared mailbox in Microsoft 365 need a licence?

Not while it stays under 50 GB and does not use an online archive or litigation hold. Exceeding any of those requires assigning an Exchange Online Plan 1 or Plan 2 licence to the shared mailbox.

### How long does it take to convert a user mailbox to a shared mailbox?

The `Set-Mailbox -Type Shared` command completes within minutes, after which the licence can be removed. Allow up to an hour for Outlook clients to reflect the change.

### Can I undo converting a distribution group to a Microsoft 365 Group?

No. The upgrade is one-way. To return to a distribution group you would create a new one with the same members and reassign the address after removing it from the Microsoft 365 Group.