Adding a shared mailbox to Outlook takes about a minute when it works, and the reason it usually works is automatic mapping. Once an administrator has added somebody as a member, restarting Outlook is normally all it takes. The mailbox turns up in the folder list with no configuration at all.
The part worth planning is what happens afterwards. Several people are now looking at the same inbox, which solves visibility and creates a new problem in its place: two people replying to the same enquiry, nobody replying to another, and no way to tell the two situations apart. Microsoft documents the mechanics thoroughly. The settings that surprise people, and the limits that arrive later, are the useful part.
Adding it in each client
Microsoft's instructions differ by client, and the first step is the same in all of them. After an administrator adds you as a member, close and restart Outlook. The mailbox should appear on its own, and if the membership was granted very recently it can take a few minutes.
New Outlook for Windows. The shared mailbox appears in the folder pane, under a folder named Shared with me, and expanding it shows the standard folders. To add it manually, right click the account name in the folder pane and choose Add shared folder or mailbox, then type the address. The mailbox can be added before membership is granted, but it will not be usable until it is.
Classic Outlook. The manual route is longer. Go to File, then Account Settings, then Account Settings again. On the Email tab, with the correct account highlighted, choose Change, then More Settings, then Advanced, then Add. Type the shared address, confirm twice, then Next, Finish and Close.
Outlook on the web. Right click Folders in the left navigation pane and choose Add shared folder or mailbox, then type the address. For Exchange on premises mailboxes, right click the name of the primary mailbox instead.
Sending is the same everywhere. Create a new message, show the From field if it is not visible, which in new Outlook is on the Options tab under Show From, and change the From value to the shared address. Microsoft notes that recipients only ever see the shared address. When replying to something that arrived in the shared mailbox, check the From field before sending, because it is the field people forget.
The calendar comes along automatically in both new and classic Outlook. Contacts do not behave the same way: in classic Outlook the shared contact list is added under My Contacts, while Microsoft's documentation states that contacts for shared mailboxes are currently unavailable in new Outlook.
As a folder, or as an account
There are two ways to hold a shared mailbox in new Outlook, and the difference is larger than it appears. Added as a shared folder, it is a set of folders you can read and send from. Added as a separate account, Microsoft lists a specific set of capabilities that become available: notifications, an unread count, automatic replies, categories, focused inbox, message format, rules, conditional formatting, sweep, junk mail, quick steps, forwarding, retention policies, and work hours.
For a mailbox that a team actually works in, notifications and the unread count are the two that change behaviour. A shared mailbox added as a folder is silent, which means it gets checked when somebody remembers to check it.
The documentation also names what is still missing, listing granting new delegated access to a mailbox as a capability planned for a future update rather than one available today.
Settings that catch people afterwards
Each of these is documented, and each one produces a support question within the first fortnight.
Sent mail does not go where people expect. By default, messages sent from a shared mailbox are not saved to the shared mailbox's Sent Items. They are saved to the Sent Items folder of the person who sent them. That means nobody else can see what was already answered, which is the single most common cause of a duplicate reply. An administrator can change it in the admin centre under the shared mailbox's Sent items settings. This should be done on day one.
Automatic replies are text only. They are configured by an administrator on the shared mailbox, and Microsoft's guidance states that images cannot be added, only text.
Hiding the mailbox from the address list has a side effect. A hidden shared mailbox still receives mail, but Microsoft warns that hiding it makes it impossible for new members to add the mailbox to their Outlook profile until it is shown again.
A new mailbox can refuse to send for about an hour. The error says you do not have permission to send on behalf of the specified user. Microsoft attributes this to replication latency across data centres and says it resolves in around an hour.
Mail from a shared mailbox cannot be encrypted. Because the mailbox has no security context of its own, it cannot be assigned an encryption key. Microsoft also notes that if members encrypt messages with their own keys, other members might not be able to read them.
Deletion cannot be prevented. Microsoft states plainly that you cannot stop users deleting messages in a shared mailbox, and recommends a Microsoft 365 group where that restriction is required.
The limits that arrive later
| Limit | Value |
|---|---|
| Storage without a licence | 50 GB |
| Storage with a licence | 100 GB, with an Exchange Online Plan 2 licence assigned to the mailbox |
| Users supported | A maximum of 25 |
| External access | Not possible. Only people inside the organisation can use a shared mailbox |
| Licence needed to access it | The person accessing it needs their own licensed Exchange Online mailbox |
| Mailboxes created before July 2018 | Already 100 GB, even unlicensed |
The storage limit behaves in a way worth knowing in advance. Microsoft's warning is that when a shared mailbox reaches its storage limit it can keep receiving mail for some time but cannot send, and after a further period it stops receiving, at which point senders get non delivery receipts. For a mailbox that has been collecting enquiries with attachments for three years, that sequence can start without anyone noticing the first stage.
The 25 user figure is a support boundary rather than a hard block. Microsoft's wording is that a shared mailbox supports a maximum of 25 users, and that too many simultaneous users may see connection failures or duplicated messages, with a Microsoft 365 group recommended above that number.
One more piece of setup worth knowing: forwarding all mail from a shared mailbox to another address or a distribution group does not require a licence on the mailbox.
Permissions, and the three things they control
Membership and permissions are managed by an administrator in the Microsoft 365 admin centre, under the shared mailbox's Members and its mailbox permissions. Three separate things are being granted, and conflating them causes most of the confusion about why somebody can read but not send.
Full access lets a person open the mailbox and work in its folders. Send as makes mail appear to come from the shared address itself, which is what a support or enquiries mailbox normally wants, since Microsoft's description of the feature is that users can send as or send on behalf of the mailbox. Send on behalf of shows both names to the recipient, in the form of one person sending for the mailbox, which is appropriate for an assistant and usually not for an enquiries address.
Two further points are worth settling at the same time. The mailbox has its own user account with a system generated password, and Microsoft's instruction is to block sign in for that account and keep it blocked, so nobody should ever be handed credentials for it. And the apps that can reach the mailbox are configurable in the same place, under Email apps, which is where to look when a mailbox opens in one client and not another.
Shared mailbox, Microsoft 365 group, or forwarding
Microsoft's documentation points at a Microsoft 365 group in three specific situations, and each is a real decision point rather than a preference.
If access is needed by people outside the organisation, a shared mailbox cannot do it, and a group is the suggested alternative. If more than 25 people need to work in it, a group is again the recommendation. And if deletion has to be restricted, a group is the only one of the two that can do it, since deletion in a shared mailbox cannot be prevented.
Forwarding is the third option and it is often the right one for a low volume address. Forwarding all mail from a shared mailbox to a person or a distribution group requires no licence on the mailbox, and it is configured in the same admin centre screen. What forwarding loses is the shared history: once mail is in individual inboxes, nobody can see what anyone else did with it.
What it does not do, and why people search again
A shared mailbox answers the question of who can see the mail. It does not answer any of the questions a team asks once more than two people are involved.
Read and unread is the only state available, it is one bit of information, and in a shared mailbox one person opening a message changes it for everybody. There is no owner, so every message is either everybody's job or nobody's. There is no record of when a reply was sent, other than searching somebody's Sent Items, and by default that is exactly where the reply went. There is no way to mark something as waiting on the other party, so a message that is genuinely blocked looks the same as one that has been ignored.
None of that is a defect. A mailbox is for messages, and it does the job it was designed for. The gap appears when the mail arriving is not conversation but intake: applications, enquiries, requests, registrations. Those arrive as a queue, they each need a decision and a reply, and a queue needs a state and an owner per item. That is a different kind of tool, and the features that matter for it are the ones that work on a submission after it arrives rather than on the message itself.
Categories and rules narrow the gap and do not close it, because both are per person conventions. The test is simple: ask two members of the mailbox to produce a list of everything still waiting for a reply, separately, and compare the lists.
What to change first
Change the sent items setting today, so that replies sent from the shared address are visible to everyone rather than sitting in one person's Sent Items. Then count how many messages currently in the mailbox are intake rather than conversation. If that is most of them, the queue needs a state and an owner per item, which is what Halict is built for, and the mailbox can go back to being a mailbox.
Q1. Why has the shared mailbox not appeared in Outlook after being added?
Automatic mapping can take a few minutes, so close and restart Outlook first. If it is still missing, add it manually: in new Outlook right click your account name and choose Add shared folder or mailbox, and in classic Outlook go through File, Account Settings, the Email tab, Change, More Settings, Advanced and Add.
Q2. Why can nobody else see the replies that were sent from the shared mailbox?
By default, mail sent from a shared mailbox is saved to the sender's own Sent Items rather than the shared mailbox's Sent Items. An administrator can change this in the admin centre under the mailbox's Sent items settings.
Q3. Does a shared mailbox need a licence?
Not for up to 50 GB of storage. Raising the limit to 100 GB requires an Exchange Online Plan 2 licence assigned to the mailbox, and litigation hold or a larger archive have their own licence requirements. The people accessing the mailbox each need their own licensed Exchange Online mailbox.
Q4. Can someone outside the organisation be given access to a shared mailbox?
No. Microsoft states that only people inside the organisation can use a shared mailbox, and that a Microsoft 365 group should be considered where external access is needed.
Q5. How many people can share one mailbox?
A shared mailbox supports a maximum of 25 users, and beyond that connection failures or duplicated messages become likely. A Microsoft 365 group is the documented alternative for a larger number of people.
Q6. Should a shared mailbox be added as a folder or as an account?
As an account, if the team works in it daily. Added that way it supports notifications, an unread count, automatic replies, rules, categories and retention policies, none of which are available when it is only a shared folder.