Microsoft 365 Shared Mailboxes

A Shared Mailbox is the mailbox a team works out of together — support@, billing@, info@. Microsoft 365 gives it an address and a folder tree, but no password of its own: people reach it through their personal Microsoft accounts, and Exchange decides who may open it.

A Shared Mailbox is the mailbox a team works out of together — support@, billing@, info@. Microsoft 365 gives it an address and a folder tree, but no password of its own: people reach it through their personal Microsoft accounts, and Exchange decides who may open it.

MailDesk connects a shared mailbox the same way Outlook does — through a member's login — and that single fact explains every requirement on this page.

How it works, in plain terms

When a colleague clicks Connect Microsoft Graph (OAuth), they sign in as themselves. Microsoft hands MailDesk a token that belongs to that person. Two things then have to be true for the shared mailbox to be readable:

1. Exchange must allow it. The signing-in person needs Full Access to the shared mailbox — that is Microsoft's own permission, granted in the admin center.
2. The token must be allowed to leave its owner's mailbox. A plain Mail.Read permission only ever reaches the signed-in person's own mail, no matter what Exchange permits. Reading somebody else's mailbox needs the .Shared variant of the permission.

MailDesk also has to ask for the right mailbox. Microsoft's /me endpoint always means "the mailbox of whoever signed in" — it can never point at a shared mailbox, regardless of permissions. That is why the account form has an explicit switch: when M365 Shared Mailbox is enabled, MailDesk addresses the mailbox by its own address instead of /me.

What you need before you start

The permission to grant

Grant the Delegated permission that matches your edition. The shared variant is additional — keep the plain one as well:

Pro needs the read-write variants because it writes back to the mailbox: marking messages read, moving them, and deleting them all happen on the server. Basic never writes to the mail server, so read permission is enough.

Connecting the mailbox

1. Create the mailbox account in MailDesk as usual (Settings → MailDesk → Mailbox Accounts → New), and put the shared mailbox's address in Email Address — for example [email protected].
2. Choose the Outlook / Microsoft 365 provider and select your Graph application.
3. Tick M365 Shared Mailbox.
4. Click Connect Microsoft Graph (OAuth).
5. In the Microsoft account picker, sign in with your own account — not the shared address, which has no password and cannot sign in.

MailDesk verifies the connection before saving anything: it asks Microsoft for the shared mailbox and only stores the credentials if the answer comes back. If it does not, the error names the cause — missing admin consent for the .Shared permission, missing Full Access in Exchange, or a sign-in with the wrong account.

After connecting, the account form shows Connected Microsoft Identity — the person whose login currently carries the connection. It is worth a glance whenever something stops working: if that colleague leaves the company or loses Full Access, the connection stops with them.

Giving your team access inside MailDesk

Exchange decides who may reach the mailbox; MailDesk decides who sees it in the app. On the account form, tick Shared Mailbox and list the colleagues under Users with Access. Only those users see the mailbox in their MailDesk sidebar — Security & access rights explains the model in full.

The two settings answer different questions and are both needed:

• M365 Shared Mailbox — how MailDesk talks to Microsoft (address the mailbox explicitly, request the .Shared permission).
• Shared Mailbox + Users with Access — who in your Odoo sees the mailbox.

Sending from a shared mailbox

Reading and sending travel different roads. Incoming mail arrives over the Graph connection described above; outgoing mail leaves through the account's Outgoing SMTP Server and is independent of it. So a shared mailbox needs both: a working Graph connection to read, and valid Microsoft 365 SMTP credentials to send.

Microsoft also treats the two as separate permissions. Full Access lets a member read the mailbox; sending as the shared address additionally requires Send As (or Send on Behalf), granted in the Exchange admin center under Delegation. Without it, Microsoft accepts the connection and shows the mail — but rejects outgoing messages that claim the shared address as the sender.

When something does not work

Outlook setup covers the Azure application itself, and Troubleshooting — setup & sync covers connection problems that are not specific to shared mailboxes.