Shared Mailboxes
Manage shared mailboxes used by teams and departments. Shared mailboxes allow multiple users to access a common mailbox without requiring a dedicated license.
Note: Shared mailboxes under 50 GB don’t require a license. For mailboxes over 50 GB, or to enable archive/litigation hold, assign an Exchange Online Plan 2 license.
Shared Mailbox List
View all shared mailboxes:
| Column | Description |
|---|---|
| Display Name | Friendly name (e.g., “Sales Team”) |
| Email Address | Primary SMTP address |
| Size | Current mailbox usage |
| Members | Number of users with access |
| Send As | Users who can send as this mailbox |
| Auto-mapping | Auto-appears in Outlook for members |
| Created | Creation date |
Creating a Shared Mailbox
Click “Create Shared Mailbox” and configure:
Display Name
Required. Descriptive name like “Support Team” or “HR Department”.
Email Address
Required. The mailbox address (e.g., support@company.com).
Members
Users or groups who will have Full Access to the mailbox.
Send As Permissions
Users who can send email appearing to come from this mailbox.
Auto-mapping
If enabled, mailbox automatically appears in Outlook for members. Disable for mailboxes accessed via separate Outlook profile.
Permission Types
Full Access
User can open the mailbox, read all messages, and manage the mailbox contents. Does NOT grant Send As permission. With auto-mapping, mailbox appears automatically in Outlook. Without auto-mapping, user must manually add as additional account.
Send As
User can send email that appears to come FROM the shared mailbox. Recipients see the shared mailbox address as the sender. No indication that a different user actually sent the message.
Send on Behalf
User can send email on behalf of the shared mailbox. Recipients see “User Name on behalf of Shared Mailbox” as the sender. Provides transparency about who actually sent the message.
Common Use Cases
- Support/Help Desk — support@company.com monitored by IT team
- Department Inbox — hr@company.com, sales@company.com
- Project Teams — Temporary mailbox for project communication
- Info/Contact — info@company.com for general inquiries
- Former Employees — Convert user mailbox to shared for access
Mailbox Settings
Email Forwarding
Forward copies of incoming messages to another address.
Automatic Replies (OOF)
Configure out-of-office responses for the shared mailbox.
Sent Items Behavior
Store copies of sent items in the shared mailbox’s Sent Items folder (not just the sender’s personal Sent Items).
Email Aliases
Add additional email addresses that deliver to this mailbox.
Hide from GAL
Hide from Global Address List if mailbox shouldn’t be discoverable.
Convert User Mailbox
When an employee leaves, convert their mailbox to shared:
- User mailbox becomes shared mailbox (preserves all content)
- Remove the M365 license (cost savings)
- Grant access to manager or replacement
- Optionally set up forwarding to replacement
Note: Conversion preserves mailbox data but removes mobile device partnerships and connected accounts. Calendar sharing permissions are also removed.
Limitations
- Cannot sign in directly — must access through delegated permissions
- 50 GB limit without license (100 GB with Exchange Plan 2)
- No mobile app support for direct access
- Archive mailbox requires license
- Litigation hold requires license
- Cannot use for SMTP relay/application sending
API Reference
GET /api/email-and-collab/exchange/mailboxes?type=shared
List all shared mailboxes
POST /api/email-and-collab/exchange/mailboxes/shared
Create new shared mailbox
POST /api/email-and-collab/exchange/mailboxes/:id/convert
Convert user mailbox to shared
POST /api/email-and-collab/exchange/mailboxes/:id/permissions
Add member permissions