A shared mailbox is a Microsoft 365 mailbox with its own address, such as support@ or info@, that several licensed users open from their own Outlook accounts. It costs nothing up to 50 GB and an admin creates it in a few minutes. A shared inbox tool connects to that mailbox and adds what it leaves out: an owner for each thread, internal notes, collision detection and reporting.
Keep the shared mailbox while it works. Three signs it has stopped: two people reply to the same client, a thread waits because each assumed the other had it, and replies scatter across Sent Items folders. The third has a two-line admin fix, covered below. The first two need a tool that connects to the mailbox, such as Sektra.
We build Sektra, which connects to Microsoft 365 shared mailboxes. The Microsoft facts in this article are from Microsoft Learn, checked in October 2026. This post is also the hub for our Outlook guides, so each section links to a deeper one where it exists.
What a shared mailbox means in Outlook
In Outlook, a shared mailbox means one mailbox with its own address that a group of people open and reply from, not a mailbox owned by one person. Microsoft 365 creates it without a license, and everyone with access sees the same messages, folders and calendar.
What is a shared mailbox in Outlook?
A shared mailbox is an Exchange Online mailbox that is not tied to one person. An admin creates it, gives members permissions, and the mailbox appears in each member's Outlook next to their own. Members read it and reply from it, and they see one another's replies once the Sent Items setting below is on. Each shared mailbox also comes with a shared calendar.
Permissions come in three kinds. Full Access lets a member open the mailbox and work in it. Send As lets a member send mail that appears to come from the shared address. Send on Behalf shows both names, as in John on behalf of Reception. Full Access on its own does not allow sending.
The difference from a user mailbox is ownership. A user mailbox belongs to one licensed person who signs into it. A shared mailbox has no license of its own, its sign-in is blocked by default, and only people inside your organization can be members. For how it differs from a distribution list or a Microsoft 365 group, see shared mailbox vs distribution list.
How do you create a shared mailbox in Microsoft 365?
Sign in to the Microsoft 365 admin center as a user with the Exchange admin role. Go to Teams & groups, then Shared mailboxes, and select Add a shared mailbox. Enter a name, which also sets the address, and select Save changes. After a few minutes, select Add members to this mailbox under Next steps and pick the people who will work it.
Members see the mailbox in Outlook after they close and restart it, because automapping is on by default. If it does not appear, see how to add a shared mailbox in Outlook. The same guide covers the web, a Mac and a phone.
The rest of the setup has its own guide in each case.
- How to create a shared mailbox in Microsoft 365 covers the admin center steps, the PowerShell equivalent, and converting a user mailbox when someone leaves.
- How to send email from a shared mailbox in Outlook covers the From field, Send As and Send on Behalf, and the Sent Items fix in full.
- Outlook shared mailbox limits, licensing and best practices covers the 50 GB ceiling, the 25-user maximum, rules, and a category scheme that holds.
- Shared mailbox vs distribution list covers when a group address should be a mailbox, a list or a Microsoft 365 group.
- How to create an email group in Outlook covers contact groups and distribution lists for cases where nobody needs to own a reply.
Why are emails sent from a shared mailbox not in its Sent Items?
By default, a reply sent as or on behalf of a shared mailbox is saved to the Sent Items folder of the person who sent it. Microsoft's own wording is that messages sent from the shared mailbox aren't saved to the Sent Items folder of the shared mailbox. Two mailbox settings control this, MessageCopyForSentAsEnabled and MessageCopyForSendOnBehalfEnabled, and both are off on a new shared mailbox.
The fix is two lines in Exchange Online PowerShell: Set-Mailbox support@yourdomain.com -MessageCopyForSentAsEnabled $true and Set-Mailbox support@yourdomain.com -MessageCopyForSendOnBehalfEnabled $true. Without PowerShell, open the mailbox under Teams & groups, Shared mailboxes in the admin center, select Edit under Sent items, and turn on both options. From then on a copy lands in the shared mailbox's Sent Items as well as the sender's.
If a member still sees nothing, check which Outlook they use. New Outlook follows the mailbox setting only. Classic Outlook for Windows also has a DelegateSentItemsStyle registry value, which moves the copy and needs Cached Exchange Mode. Send email from a shared mailbox in Outlook has the table of what each combination does.
The fix shows the team what was sent. It cannot show who sent it, since Send As hides the person, and it adds no place for the note that explains why.
What does a shared mailbox do well?
Quite a lot, for no money. Everyone sees the same mail. Replies go out from the shared address, so the client sees one identity. Permissions live in one place and an admin manages them. It works in Outlook on Windows, Mac, the web and mobile, and the shared calendar comes with it.
Categories, flags and folders give a team a light way to mark state, and rules can sort incoming mail. A small team with modest volume and an agreed category scheme can run a support address this way for years.
Where does a shared mailbox stop?
1. Nobody owns anything
A shared mailbox has no concept of assignment. A message is read or unread, and nothing records who read it. Teams improvise with categories named after people, or a rule that whoever opens a message owns it. Both hold until two people answer the same client on one afternoon, or nobody answers because each assumed the other had it. Two people replying to the same email is what sends teams looking.
2. The thread shows what was said, and nothing about why
With the Sent Items setting on, the team can see every reply. What it cannot see is the reasoning: the call where the client agreed to a change, the reason a discount was offered, the colleague who said to wait. There is no internal note on a message, so that context is forwarded, said out loud, or lost.
3. State is a convention
Categories and flags are shared, but they mean whatever the team agreed, and nothing enforces it. A flag that means waiting on the client to one person means follow up on Friday to another. Nothing can tell you how many threads are waiting on a reply from your side, how old the oldest one is, or who is carrying the most.
4. It holds messages and remembers nothing about the relationship
Every message a client ever sent is in there, and that is all that is in there. The promise made in a March thread is in there. So is the question in paragraph three that never got an answer, and the client who wrote weekly and has not written in a month. Nothing surfaces any of it. Search finds what you already know to look for.
5. The practical limits
A shared mailbox holds 50 GB without a license, and an Exchange Online Plan 2 license raises that to 100 GB. In-place archiving and litigation hold need Plan 2, or Plan 1 with the Exchange Online Archiving add-on.
Microsoft states a maximum of 25 users, with connection failures and duplicated messages above that. Nobody outside your organization can be a member, direct sign-in is blocked, and mail from the address cannot be encrypted, since the mailbox has no credentials of its own.
None of these is a defect. They are the edges of a feature designed for a front desk, and a team running client relationships at volume meets them. Outlook shared mailbox limits, licensing and best practices covers each one with the workaround where there is one.
Does a shared mailbox need a license?
Not for the mailbox itself, up to 50 GB. The people who use it each need a licensed Exchange Online mailbox, and the subscription has to include email, which Microsoft 365 Apps for business does not. A license is needed in three cases: more than 50 GB, in-place archiving, or litigation hold. To remove a license from a shared mailbox, use the Active users page; the Shared mailboxes page cannot change licenses.
How do you tell which side of the line you are on?
- Count the double replies and the dropped threads in the last quarter. More than a couple means ownership is the problem, and no category scheme fixes it.
- Ask how long it takes to answer where do we stand with this client. If the answer involves three Sent folders and a colleague's memory, the mailbox has stopped being a system of record.
- Look at who writes in. Mostly new names means you have a queue, and a well-run shared mailbox or a queue tool will do. Mostly the same names means you have relationships, and the mailbox is carrying context it cannot show you.
- Check the storage and the member count against the limits above. Growth alone can force the decision.
What should a shared inbox tool for Outlook do?
Many shared inbox tools grew up on Gmail, and Microsoft 365 support ranges from complete to nominal. Confirm first that the tool connects the shared mailbox itself, since some connect only individual user mailboxes. Check that it signs in through Microsoft's consent flow, with no password stored, and that it handles the admin consent step some tenants require.
Then the practical questions. Do categories and flags keep their meaning on both sides? Does the shared mailbox stay in Microsoft 365 with the tool connected to it, so that leaving is a disconnect and no migration? After that the questions are the same for Outlook and Gmail teams. Ownership and assignment, internal notes on the thread, collision detection, reporting, and whether the tool keeps any record of the client beyond the messages.
Where Sektra fits
Sektra connects Microsoft 365 mailboxes, including shared mailboxes, through Microsoft sign-in, so Sektra never sees the password, and the shared mailbox stays in Microsoft 365 underneath. Where a tenant requires admin consent, Sektra shows the exact request to forward. Categories map to tags, flags to stars, and read state moves both ways, so a colleague who only ever opens Outlook sees the same state.
On top, every thread has an owner and internal notes, and when two people open the same thread the inbox shows A teammate is typing a reply. The memory layer, the record Sektra builds per client from the existing mailbox history, holds the commitments made in either direction, the open questions, and the people involved.
A watch, a silence alert with a day count you set, tells you the day a client goes quiet, and the morning digest lists who owes you a reply. The Outlook integration page covers categories, Focused Inbox and consent. The help article on connecting an Outlook shared mailbox has the click-by-click steps, and the product page covers the rest.
Firms in legal and accounting, where Microsoft 365 is standard and the same clients write for years, are the shape of team this is built for.
Keep the shared mailbox if it is working. The moment to look further is when the team is paying for its limits in double replies, dropped threads and clients nobody remembered to check on. By then the mailbox has a cost, even if nothing invoices it.
