A shared mailbox is a single Exchange Online inbox that several people open (info@, finance@, jobs@). A distribution group (distribution list) is an address that copies incoming mail to each member’s own mailbox. A Microsoft 365 group is a membership object in Entra ID that includes a group mailbox, a calendar, a SharePoint site, and often a Team.
They all have an email address. They are not interchangeable.
Which object for which job
| Need | Use | Why |
|---|---|---|
| One inbox everyone works from, with a shared sent history | Shared mailbox | Mail stays in one store. Members get Full Access and usually Send As. |
| An announcement list that should land in each person’s inbox | Distribution group | No shared store. Each member files or deletes their own copy. |
| An ongoing team with files, chat, and a group mailbox | Microsoft 365 group / Team | Membership is reused across mail, files, and Teams. |
| A person who is away, not a department address | Delegate on the user mailbox, or a shared mailbox you already have | Do not create a distribution group named after one staff member. |
A shared mailbox in Microsoft 365 does not need its own paid user licence under common Microsoft conditions (size and usage limits still apply). A distribution group is not a mailbox; it cannot hold mail when members are removed.
Send As on a shared mailbox is how outgoing mail shows info@ instead of the person’s address. Send on Behalf shows “Jane on behalf of info.” Pick one and tell the team. SPF, DKIM, and DMARC still apply to the domain; they do not change because the mailbox is shared.
Standing up a department inbox
- Create a shared mailbox (not a licensed user) for the address
- Grant Full Access and Send As to a named Entra ID group of staff
- Have each person add the mailbox in Outlook, not share a password
- Agree who owns unanswered mail on a given day
- Remove access on the same day as a leaver’s user account
Groups, nesting, and noise
Distribution groups can nest (a group inside a group). Deep nesting makes it hard to see who will receive a message. Prefer flat, named lists (“All JB plant,” “All KL office”) over “Everyone” plus hidden exceptions.
A Microsoft 365 group has a conversation history in the group mailbox. People who never open that mailbox will miss mail unless they also subscribe to copies. Teams-first organisations often let the channel carry the discussion and keep the group mailbox for external senders.
Exchange Administrators create these objects. Site owners cannot invent a shared mailbox from a SharePoint screen.
What goes wrong
Sharing the password of a licensed dummy user (“the info account”) bypasses audit and MFA. When that password leaks, the dummy user is a full sign-in. A shared mailbox plus individual sign-in is the intended model.
Auto-mapping in Outlook can attach a shared mailbox automatically after Full Access. If it does not, add it once. Do not create a second shared mailbox “because Outlook did not show it.”
A practical example
Sales uses a distribution list leads@ that drops every enquiry into six inboxes. Two people reply, four delete the mail, and nobody sees the sent thread. The revision creates a shared mailbox leads@, gives the six people access, and keeps a separate distribution group all-sales@ only for internal announcements.
Key takeaways
- Shared mailbox = one inbox. Distribution group = fan-out to personal inboxes.
- A Microsoft 365 group is membership plus mailbox, files, and often a Team.
- Do not share a dummy user’s password. Use Full Access and Send As.
- Remove mailbox access when you disable the person’s account.
FAQ
Can a shared mailbox sign in to Teams?
A shared mailbox is not a person. People sign in as themselves and open the mailbox. A Team is the right place for chat.
How many people can use one shared mailbox?
Enough to cover the hours, few enough that ownership is clear. If twenty people “watch” info@, nobody does. Split by function (jobs@, support@) before you add more watchers.
Should every department get a Microsoft 365 group instead?
If they already work in Teams and share files, the group may already exist. Add a shared mailbox only when you need a dedicated inbox that is not the group’s conversation store.