A shared mailbox in Microsoft Exchange is a mailbox that belongs to a role, like office@ or billing@, and not to a person. Nobody signs in to it. Each of you opens it from your own Outlook, using permissions an admin grants you by name. A regular mailbox belongs to one person, has its own sign-in and needs its own license. A shared mailbox needs no license up to 50 GB, as long as everyone who opens it has a licensed mailbox of their own. That’s the whole difference, and the rest of this page is what it means in practice. Everything below was checked against Microsoft’s own documentation on October 4, 2026.
If you’re setting one up for a firm of two or three, you’ll need about half an hour. Ten minutes to create it, a few to grant permissions, and the rest waiting for Outlook to catch up.
How a shared mailbox differs from your own mailbox
In Outlook the two look almost the same. You see an inbox, folders and a calendar. The differences sit underneath.
| Exchange shared mailbox | Regular user mailbox | |
|---|---|---|
| Belongs to | A role or address | One person |
| Sign-in | Blocked by default, reached through members’ own accounts | Its own username and password |
| License | Free until it passes 50 GB | Each person pays for theirs |
| Who can open it | As many as 25 colleagues, all inside the firm | Its owner and any delegates |
| Replies come from | The shared address, or “you on behalf of” it | The person |
| Encrypted sending | Can’t be done | Supported |
| Where your sent replies land | Your own Sent Items, unless an admin changes it | Its own Sent Items |
Microsoft’s about shared mailboxes page is the source for every row but the last. The last row comes from a Microsoft troubleshooting article, and it’s the one that surprises people. There’s a fix for it below.
Microsoft lists the usual jobs for a shared mailbox as company information addresses, support addresses and reception or front-desk mailboxes. For a small firm, that’s info@, office@ or hello@.
Is Exchange mail the same as Outlook?
They’re two halves of one thing. Exchange is the mail server. In Microsoft 365 it’s called Exchange Online, and it holds your mailboxes, calendars and permissions. Outlook is the app you read them in, on Windows, Mac, the web or your phone. A shared mailbox lives in Exchange. Outlook is just one of the windows onto it. That’s why the admin steps below happen in an admin center, and the everyday steps happen in Outlook.
What to settle before you create one
A few limits decide whether a shared mailbox fits. They take five minutes to check.
- Your plan includes email. Microsoft says “The Microsoft 365 Apps for business subscription doesn’t include email.” Business Basic, Standard and Premium do.
- Everyone who’ll open it has a licensed mailbox. The shared mailbox is free. The people using it aren’t.
- Everyone is inside the firm. Microsoft says you can’t give people outside your business, “such as people with a Gmail account”, access. An outside bookkeeper needs a Microsoft 365 group instead.
- It’ll stay under 50 GB, or you’ll license it. Past 50 GB, an Exchange Online Plan 2 license raises the cap to 100 GB. Archiving and litigation hold need Plan 2, or Plan 1 with the Exchange Online Archiving add-on.
- You don’t need to send encrypted mail from it. If you do, send sensitive mail from a named person’s own mailbox.
- You’re sure you don’t want a group. Microsoft says “It’s not possible to migrate a shared mailbox to a Microsoft 365 group.”
The storage limit is the one with a real consequence. Here’s how Microsoft describes it:
When a shared mailbox reaches the mailbox storage limit, you can receive email for some time, but you can’t send new email. After some time, the shared mailbox stops receiving email and senders to the mailbox receive a non-delivery receipt.
So an info@ that has quietly gathered years of attachments deserves a size check now and then. One detail helps older firms. Microsoft says unlicensed shared mailboxes created before July 2018 have 100 GB. Microsoft changes these limits from time to time, so check the page again before you plan around them.
How to create a shared mailbox in Microsoft 365
You’ll need someone with the Exchange admin role. In the Microsoft 365 admin center:
- Go to Teams & Groups, then Shared mailboxes. Select Show all if you don’t see Teams & Groups.
- Select Add a shared mailbox and type a name. The name sets the address, and you can edit it.
- Select Save changes, then wait a few minutes.
- Under Next steps, choose Add members to this mailbox and add each person.
Those are Microsoft’s steps from create a shared mailbox. Sign-in starts blocked, and it should stay that way. Microsoft’s wording is plain: “Always block sign-in for the shared mailbox account and keep it blocked.”
If your firm still runs Exchange on its own server alongside Microsoft 365, the steps move. Microsoft says a hybrid organization “should use the on-premises Exchange admin center to create and manage shared mailboxes.”
Turning a departing colleague’s mailbox into a shared one
This is the other common way a small firm gets a shared mailbox. Someone leaves, clients keep writing to them, and you want the history kept without paying for their seat. Microsoft’s convert a user mailbox page covers it.
- Leave their license on for now. Without one, the convert option doesn’t appear.
- In the admin center, go to Users, then Active users, and select the person.
- On the Mail tab, select Convert to shared mailbox, then Convert.
- Reset their password. Microsoft warns that otherwise “the original username and password will continue to work on the shared mailbox.”
- Add the people who’ll cover it as members.
- If it’s under 50 GB, remove the license. Don’t delete the account, because the shared mailbox needs it as an anchor.
All existing mail, calendar items and inbox rules come across. You can convert it back to a regular mailbox later from the Exchange admin center.
Full Access, Send As and Send on Behalf
Members added in the admin center get what they need to read and reply. Behind that are three separate permissions. Knowing them is how you fix a mailbox that opens but won’t send.
| Grants | On the client’s screen | |
|---|---|---|
| Full Access | Reading, filing, deleting and the calendar | No reply at all, since this one can’t send |
| Send As | Replies in the firm’s name | office@yourfirm.com and nothing else |
| Send on Behalf | Replies that name the writer | “John on behalf of Reception Building 32”, in Microsoft’s example |
Microsoft spells out the catch with the first one:
However, a user with Full Access permission can’t send email from the shared mailbox unless they also have Send As or Send on Behalf permission.
Each member therefore needs two things: Full Access, and a way to send. Send As puts every reply in the firm’s name. Send on Behalf adds the writer’s name beside the firm’s. Pick one for everyone, so clients see the same thing whoever answers.
To check or change them, an admin goes to the Exchange admin center:
- Open Recipients, then Mailboxes, and select the shared mailbox.
- Under Mailbox permissions, choose Manage mailbox delegation.
- Add or remove people for Full Access, Send As or Send on Behalf.
- Save.
Grant each permission to people by name. If you grant it through a security group, the mailbox won’t appear in Outlook on its own, because automapping only follows names.
Adding the shared mailbox in Outlook
Where it shows up depends on which Outlook you use. Classic Outlook usually finds it without you doing anything. The others need one step.
| Outlook | How the shared mailbox arrives | How you send from it |
|---|---|---|
| Classic Outlook for Windows | Appears on its own after a restart | Change the From field |
| New Outlook for Windows | You add it once | Change the From field |
| Outlook on the web | You add it once, or open it in its own tab | More actions, then Show From |
| Outlook for iPhone and Android | You add it once as a shared account | Switch to the shared account first |
| Outlook for Mac | You open it as a shared folder | Change the From field |
Classic Outlook for Windows
Close Outlook and open it again. With automapping on, which is Microsoft’s default, the shared mailbox appears under your own in the folder pane. Its calendar joins your calendar list too.
If it doesn’t appear, add it by hand. These are the steps from Microsoft’s open and use a shared mailbox in Outlook:
- The setting lives under File, then Account Settings, then Account Settings again.
- On the Email tab, it’s your own account you change, using Change.
- From there it’s More Settings, then the Advanced tab.
- The list is called Open these additional mailboxes, and Add puts the shared address on it.
- OK takes you back to Outlook.
There’s a third way, and it’s the one to use if you want calendar reminders. Classic Outlook only shows event reminders for a shared mailbox when it’s added as a separate account, per Microsoft’s additional account article. Choose File, then Add Account, and type the shared address. When it asks you to sign in, use your own address and password. If the mailbox was automapped first, an admin has to turn automapping off for you. Then wait up to an hour before adding it, or you’ll see it twice.
New Outlook for Windows
In the folder pane, right-click your account name and choose Add shared folder or mailbox. Type the shared address and select Add. The mailbox appears under Shared with me, and its calendar joins your list.
Two limits apply. Microsoft says contacts for shared mailboxes are “currently unavailable in new Outlook.” And new Outlook doesn’t support on-premises Exchange accounts at all, so a firm on its own Exchange server stays on classic Outlook or the web.
Outlook on the web
In Outlook on the web, the option is on the right-click menu of Folders in the left pane. It’s called Add shared folder or mailbox, and it asks for the shared address. To keep the shared mailbox apart, Open another mailbox under your profile picture puts it in its own browser tab.
To send as the shared address, start a message, choose More actions, then Show From. Remove your address from the From field and type the shared one.
One thing the web can’t do for members is automatic replies. Microsoft says “Only your Microsoft 365 admin has permissions to set this up.” So the holiday-closing message on office@ is a job for whoever holds the admin role.
Outlook on iPhone and Android
The Outlook app handles shared mailboxes. These are the steps from Microsoft’s add a shared mailbox to Outlook mobile:
- Sign in to your own account in Outlook for iOS or Android.
- Tap Add Account in the left pane, then Add a Shared Mailbox.
- If you have several accounts in the app, pick the one that has access.
The shared mailbox then sits in your account list like a separate account. Tap it to read and reply from it. To remove it, go to Settings, then Accounts, select it and choose Delete Account.
Here’s what doesn’t work on a phone:
- The iPhone’s own Mail app, and Android’s built-in mail apps. Microsoft says a shared mailbox “can only be added to Outlook for iOS app or the Outlook for Android mobile app.”
- Anything not in Exchange Online. Both your mailbox and the shared one have to be in Microsoft 365.
- Signing in as the shared address. Sign-in is blocked by design, so you always come in through your own account.
Anywhere the Outlook app won’t go, the phone’s browser and Outlook on the web still reach the shared mailbox.
Outlook for Mac
On a Mac, the shared mailbox opens as a shared folder from your own account. Microsoft’s Outlook for Mac steps walk through it.
When Outlook won’t send from the shared mailbox
This is the most common shared mailbox complaint. Work down the list in order. Most cases stop at the first or second item.
- It’s new, or you were just added. Microsoft says the error “You do not have the permission to send the message on behalf of the specified user” comes from replication. It “goes away in about an hour.” Wait, then try again.
- You have Full Access and nothing else. You can read the mailbox but not send from it. Ask your admin to add Send As or Send on Behalf.
- The mailbox is hidden from the address list. Microsoft says Send As and Send on Behalf “do not work in the Outlook desktop client” when the shared mailbox is hidden from the Global Address List. That note covers the desktop app, so trying the same send on the web is a quick test. Your admin can unhide it.
- The From field still shows you. Replying inside the shared mailbox doesn’t always switch it. Pick the shared address in From before you send. If it isn’t listed, choose Other email address and type it.
- The mailbox is full. At 50 GB without a license, sending stops first. Clear out large attachments, or license it.
- Your Outlook profile is stale. In classic Outlook, close and restart after any permission change. If it still fails, try the same send from Outlook on the web. If the web works, the problem is the desktop profile, and the permissions are fine.
Where your replies from the shared mailbox end up
By default, a reply you send from the shared mailbox is filed in your own Sent Items. Your colleague opens the shared mailbox, sees the client’s message and no answer, and may answer it again. Microsoft’s troubleshooting article explains why. You sign in to your own mailbox and send from there, so Outlook files the copy where you are.
An admin can change this once for the whole mailbox, in Exchange Online PowerShell. For replies sent as the shared address:
Set-Mailbox office@yourfirm.com -MessageCopyForSentAsEnabled $trueAnd for replies sent on behalf of it:
Set-Mailbox office@yourfirm.com -MessageCopyForSendOnBehalfEnabled $trueAfter that, a copy of every reply also lands in the shared mailbox’s own Sent Items. Each of you can see what’s been answered. Microsoft notes this is the only method that works in new Outlook. For a mailbox two or three people answer, it’s the single most useful setting to turn on.
A shared mailbox or a Microsoft 365 group in Outlook
Microsoft 365 offers a second kind of shared address, the Microsoft 365 group. In Outlook it shows up under Groups and not as a mailbox. It’s built for a team that works together on files and a calendar, as well as mail.
| Shared mailbox | Microsoft 365 group | |
|---|---|---|
| Built for | One address several people answer | A small team working together |
| One copy everyone reads | A group inbox, and members can also get each message in their own inbox | |
| Files, Planner and Teams | No | Yes |
| People outside the firm | No | Yes, if your admin allows guests |
| Replying as the address | Send As or Send on Behalf | Send As or Send on Behalf, if your admin enables it |
| More than 25 people | No | Yes |
The source is Microsoft’s compare groups page. For office@ at a three-person firm, the shared mailbox is the simpler fit. Choose the group when files and a Teams channel should travel with the address, or when someone outside the firm needs in. The team email guide takes that choice further, alongside aliases and distribution lists.
A distribution list is the third option people meet. Microsoft describes it as best for when you “need to broadcast information to a set group of people”. It copies each message to everyone, so it suits announcements and not an address you answer.
What a shared mailbox leaves to the two of you
A shared mailbox gives you one address, one copy of each message, one calendar and replies in the firm’s name. That covers most of what a small firm needs from office@. What it doesn’t give you is any sign of who’s handling what.
- No owner on a thread. It’s easy for both of you to think the other one took it.
- No status. Waiting and done look the same in a folder.
- No record of who said what, if everyone sends as the firm.
- No limit on deleting. Microsoft says “You can’t prevent users from deleting messages in a shared mailbox.”
For two or three people, a few agreed habits cover that well. Managing a shared inbox without stepping on each other sets them out: one owner per thread, a short triage pass, and a way to stop the double reply. A shared mailbox process that holds puts the permissions and the joining-and-leaving steps on one page. If the habits stop holding, choosing shared inbox software weighs what a dedicated tool adds. And if your firm runs on Google Workspace instead, sharing one Gmail address covers the Collaborative Inbox.
Point beside a Microsoft 365 shared mailbox
If one shared address is what your firm needs, the shared mailbox above is the answer, and it’s already in your Microsoft 365 plan.
Point works on each person’s own Microsoft 365 mailbox. It doesn’t turn office@ into a shared queue. What it does is read your own mail as it lands, put the thread that needs you today at the top, and draft a reply in your voice. By default nothing goes out until you’ve looked at the draft and sent it yourself. What Point works out goes back into your mailbox as ordinary Outlook categories, so you see it in Outlook too. The Outlook path explains what a Microsoft 365 connection covers, and how Point works shows a day with it.
Seats are per person, so each colleague connects their own account. Per-seat billing explains how that’s counted.
Common questions
What is the difference between a shared mailbox and a regular mailbox in Microsoft Exchange?
A regular mailbox belongs to one person, has its own sign-in and needs a license. A shared mailbox belongs to an address like office@, has sign-in blocked, and is opened by members from their own Outlook. It needs no license up to 50 GB. It also can’t send encrypted mail, and it’s limited to 25 people inside your organization.
Is Exchange mail the same as Outlook?
No. Exchange is Microsoft’s mail server, called Exchange Online in Microsoft 365. Outlook is the app you read that mail in. A shared mailbox is created in Exchange and then opened in Outlook on Windows, Mac, the web or a phone.
What are the key differences between an Office 365 group mailbox and a shared mailbox?
A shared mailbox is one inbox and calendar several people answer from. A Microsoft 365 group brings a shared file library, a Planner board and an optional link to Teams. It can include outside guests, and can deliver each message to members’ own inboxes. A shared mailbox can’t be migrated into a group later, so choose before you create it.
What is the best way to manage a shared mailbox in Outlook?
Give each person Full Access plus one sending permission, granted by name. Ask your admin to turn on MessageCopyForSentAsEnabled so replies show in the shared Sent Items. Then agree who owns each thread and mark it when it’s handled. Managing a shared inbox without stepping on each other covers the habits in full.
Does a shared mailbox need a license?
Only above 50 GB, or for archiving and holds. Each person who opens it needs a licensed Exchange Online mailbox of their own. The shared mailbox needs an Exchange Online Plan 2 license to grow to 100 GB, and Plan 2 or Plan 1 with the Archiving add-on for a larger archive or litigation hold.
Why can I read the shared mailbox but not send from it?
You probably have Full Access only. Ask your admin for Send As or Send on Behalf. If you were added in the last hour, wait, because Microsoft says the permission error clears once replication catches up.
Can I add a shared mailbox to the iPhone Mail app?
No. Microsoft supports shared mailboxes only in the Outlook app for iPhone and Android, and only when both mailboxes are in Exchange Online. In the Outlook app, tap Add Account, then Add a Shared Mailbox.
How do I log in to a shared mailbox?
You don’t. Sign-in is blocked by design. You sign in to your own account, and the shared mailbox appears beside it once you have permission.