Use a shared mailbox when several people need to read, reply to and file email sent to one address, such as info@ or accounts@. Use a distribution list when you only need one address that copies a message to a fixed set of people, such as all-staff@. Use a Microsoft 365 Group when a team needs a shared inbox plus shared files and a calendar in one place.
Quick answer: In Microsoft 365, a shared mailbox is one inbox that several people work from, and replies go out from the shared address. A distribution list has no inbox of its own; it simply forwards each message to every member. A Microsoft 365 Group gives a team a group inbox, calendar, SharePoint files and Planner together. Pick by the job: answering customers, broadcasting, or running a team.
In this guide: what each option actually does, a table that matches common jobs to the right one, the limits Microsoft sets on each, and the set-up mistakes that cause bounced customer emails and confused staff later.
What each option actually does
All three give you an email address that reaches more than one person, which is why they get confused. The difference is where the message ends up and what people can do with it once it arrives.
Shared mailbox
A shared mailbox is a real mailbox with its own inbox and calendar. Nobody signs in to it directly. Instead, an administrator gives named staff permission to open it inside their own Outlook, where it appears as a second mailbox under their own. When someone replies, the customer sees the shared address, not the member of staff who wrote it, provided they have been given Send As permission.
Everyone works from the same copy of each message, so when one person files an enquiry, everyone else sees it has been dealt with.
Distribution list
A distribution list, which Microsoft also calls a distribution group, has an address but no mailbox. A message sent to it is copied into the personal inbox of every member, and there it stops being shared. If five people get a customer enquiry through a list, there are now five separate copies, and nobody can tell from their own inbox whether a colleague has already answered.
That makes lists good for broadcasting and poor for handling work. Microsoft’s comparison of group types describes distribution groups as best for sending information to a set group of people.
Microsoft 365 Group
A Microsoft 365 Group is a membership that comes with a bundle of shared tools: a group inbox for conversations, a shared calendar, a SharePoint site for files, a Planner board and a OneNote notebook. It can also sit behind a Microsoft Teams team. Email sent to the group’s address lands in the group inbox, and each member can choose to have conversations copied into their own inbox as well.
A group suits a project or department that needs to share more than email. It is a heavier tool than the other two, and creating one creates a SharePoint site with it, which is worth knowing before anyone makes a dozen of them.
Which one should you use for which job?
The quickest way to settle shared mailbox vs distribution list, or either against a group, is to ask what happens after the email arrives. If someone has to own the reply, you want a shared inbox. If people only need to read it, a list will do. If the email is one part of a wider piece of team work, look at a group.
| The job | Use | Why |
|---|---|---|
| info@, sales@ or enquiries@ that customers write to | Shared mailbox | One copy of each enquiry, replies go from the shared address, and staff can see what has been answered. |
| accounts@ for supplier invoices and remittances | Shared mailbox | Invoices need filing and a record that survives staff changes. A list leaves them scattered across personal inboxes. |
| all-staff@ for company announcements | Distribution list | Everyone needs to read it, nobody needs to reply as the company, and members change only when staff join or leave. |
| directors@ so a message reaches every director | Distribution list | A simple copy to a small fixed group. Each director keeps the message in their own mailbox. |
| A project team sharing email and files | Microsoft 365 Group | Conversations and documents live together and are handed over cleanly when the project team changes. |
| support@ answered by more than 25 people | Microsoft 365 Group | Microsoft recommends a group once a shared mailbox would need more users than it supports. |
The trouble usually starts when one option is used for another’s job, most often a distribution list standing in for a shared inbox.
When a shared mailbox is the right choice
A shared mailbox is the default answer for any address the outside world writes to and expects a reply from. It is also the cheapest option, because a shared mailbox does not need a licence of its own for normal use.
The rules are set out on Microsoft’s page about shared mailboxes, and at the time of writing they are:
- Storage: up to 50 GB without a licence. Going beyond that, or adding a larger archive or litigation hold, means assigning a licence such as Exchange Online Plan 2.
- Who can open it: each person who uses it needs their own licensed Exchange Online mailbox. People outside your organisation cannot be given access.
- How many people: Microsoft supports a maximum of 25 users. Beyond that, people may see connection failures or duplicated messages, and Microsoft suggests a Microsoft 365 Group instead.
- Sign-in: the mailbox has a system-generated password that is not meant to be used, and Microsoft’s advice is to block sign-in for the shared mailbox account and keep it blocked.
Two behaviours catch people out. First, anyone with access can delete anything, and there is no setting to stop that within a shared mailbox. If an address needs messages to be protected from deletion, that points towards a group or a retention policy. Second, when someone sends as the shared mailbox, the copy goes into their own Sent Items by default rather than the shared mailbox’s. An administrator can change that so the whole team sees what was sent, and on any customer-facing mailbox it is worth doing.
A shared mailbox is also where a leaver’s email often goes. Converting a former employee’s mailbox to a shared one keeps their history available to their manager and frees the licence, which is one of the steps in our IT offboarding checklist. Once access has been granted, staff add it in Outlook using the steps in how to add a shared mailbox in Outlook.
When a distribution list is enough
A distribution list earns its place when the message is information rather than work. Announcements and rota changes fit well. The list has no storage and needs no licence, and because each member keeps their own copy, nothing is lost if one person deletes theirs.
The setting that matters most is who may send to it. In Exchange Online the default for a new distribution list is to accept messages only from people inside your organisation. That is sensible for all-staff@, because it stops outsiders mailing your whole company. It also explains a common complaint: a list set up as sales@ that silently rejects every customer, because nobody changed the sender option to allow people outside the organisation. Microsoft’s guide to managing distribution groups covers the sender options, along with owners (every list must have at least one) and moderation.
Two other points are worth knowing. A Microsoft 365 Group cannot be a member of a distribution list, so you cannot nest a team’s group inside all-staff@. And a plain distribution list cannot be used to give people access to a SharePoint site or a folder. For that you need a security group, or a mail-enabled security group if the same membership also needs an email address.
Dynamic lists: Exchange Online also offers dynamic distribution groups, whose membership is worked out each time a message is sent, based on attributes such as department or office. They save manual upkeep on lists such as “everyone in the Crawley office”, but only if those attributes are filled in correctly on every user.
When a Microsoft 365 Group fits better
A Microsoft 365 Group is the right tool when email is only part of what a team shares. A bid team that swaps emails and keeps drafts in SharePoint is better served by one group than by a shared mailbox plus a pile of separate permissions.
Groups also cope with things shared mailboxes cannot. Guests from outside the organisation can be added if your administrator allows guest access, the group can be connected to a Teams team, and membership is managed in one place, so adding someone to the group gives them everything at once. Microsoft’s groups overview gives a group mailbox 50 GB of storage at the time of writing.
The trade-off is that a group inbox behaves more like a discussion thread than a working mailbox. Conversations live in the group, not in each person’s inbox, unless members choose to follow them there, and replying as the group address needs an administrator to grant Send As or Send on Behalf. For a busy customer-service address that needs folders and a clear “who is dealing with this” view, many teams find a shared mailbox simpler.
Be careful with sprawl. By default any user can create a group, and each one brings a SharePoint site and calendar with it. Agree who is allowed to create them, and give each one an owner and a clear name.
Set-up mistakes that cause problems later
Most of the helpdesk tickets about shared addresses trace back to a few decisions made in a hurry when the address was first created. These are the checks worth running on what you already have.
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A list doing a shared mailbox’s jobCustomer enquiries copied to several inboxes, answered twice or not at all.Check: if anyone replies as the company from an address, make it a shared mailbox.
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External senders blocked on a public addressA distribution list printed on the website that rejects mail from outside the organisation.Check: send a test from a personal email account to every address on your website and letterhead.
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Sign-in left open on a shared mailboxA shared mailbox account with a password someone set and still uses on a phone.Check: confirm sign-in is blocked on every shared mailbox account in the Microsoft 365 admin centre.
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A licence paid for by habitShared mailboxes created as full user accounts and licensed for no reason.Check: licence a shared mailbox only if it needs more than 50 GB, an archive or a hold.
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Leavers still holding accessFormer staff still listed with Full Access or Send As on accounts@.Check: review shared mailbox permissions whenever someone leaves or changes role.
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Lists and groups with no ownerNobody knows who should approve membership changes, so nobody does.Check: give every list and group a named owner who is still employed.
Shared addresses also send a lot of your outbound mail, so make sure they pass your domain’s email authentication. Our explainer on SPF, DKIM and DMARC covers why mail from info@ can land in a customer’s junk folder.
Changing your mind later is possible, but not in every direction. Exchange Online can convert a distribution list into a shared mailbox, and a user mailbox into a shared one, but Microsoft states that a shared mailbox cannot be migrated to a Microsoft 365 Group. If you think an address might grow into a team workspace, decide before the history builds up.
Frequently asked questions
Does a shared mailbox need a Microsoft 365 licence?
No, not for normal use. A shared mailbox can hold up to 50 GB without a licence of its own, but every person who opens it needs their own licensed mailbox. You need to licence the shared mailbox itself only if it needs more storage, an archive mailbox or litigation hold, at the time of writing.
Can customers email a distribution list?
Only if you allow it. A new distribution list in Exchange Online accepts mail only from people inside your organisation by default, so messages from customers are rejected. An administrator can change the sender option to accept mail from outside, but if staff need to reply as the company, a shared mailbox is usually the better fit.
Can I open a shared mailbox on my phone?
Yes. Microsoft says the Outlook apps for iOS and Android can open shared mailboxes you have been given access to. You add it from within your own account rather than signing in to the shared mailbox, because sign-in for the shared account should stay blocked.
What is the difference between a distribution list and a security group?
A distribution list only delivers email. A security group grants access to things such as SharePoint sites and folders, and has no email address unless it is a mail-enabled security group. If one membership needs both an address and file permissions, a mail-enabled security group or a Microsoft 365 Group does both jobs.
Getting shared addresses right is a small job that saves a lot of confusion as staff come and go. Our managed IT support team can review the addresses you already have.
Tidy Up Your Shared Email Addresses
We review your shared mailboxes, lists and groups, fix permissions and sender settings, and set each address up for the job it actually does.
