Give a colleague access to your Microsoft 365 mailbox or calendar, for example so an assistant can manage your diary, someone can cover your inbox while you're away, or a team can read a leaver's email. This guide explains the different permission types and how both users and administrators set them up.
Which permission do you need?
| Permission | What it allows | Who can grant it |
|---|---|---|
| Read and manage (Full Access) | Open the whole mailbox, read, file and delete mail. Does not allow sending. | An administrator |
| Send as | Send email that appears to come directly from the mailbox. Recipients can't tell someone else sent it. | An administrator |
| Send on behalf | Send email that shows "Assistant on behalf of Manager". | An administrator, or the mailbox owner by making someone a delegate |
| Calendar Delegate | Edit the calendar and receive and respond to meeting requests for the owner. | The mailbox owner |
| Folder permissions | Access to one folder, such as the calendar or a single mail folder. | The mailbox owner |
Users: share your calendar as a delegate
Outlook on the web and the new Outlook
- Open Calendar, select Share (or Share calendar) and choose your calendar.
- Enter your colleague's name and choose Delegate from the permission drop-down.
- Select Share. They get an invitation to accept. To choose whether meeting requests go to you, your delegate or both, open the calendar's Sharing and permissions after sharing and adjust the delegate settings.
Classic Outlook for Windows
- Select File → Account Settings → Delegate Access, then Add.
- Choose the colleague and set their level for Calendar, Tasks, Inbox and Contacts (for example Editor for calendar).
- Choose how meeting requests are delivered at the bottom of the Delegate Permissions window and select OK.
A delegate automatically gets Send on behalf for meeting requests. For calendar viewing only, use normal calendar sharing instead. See Share your calendar.
Admins: give someone access to a whole mailbox
- Sign in to admin.microsoft.com and go to Users → Active users.
- Select the mailbox owner's name, then the Mail tab.
- Under Mailbox permissions, choose the type you need: Read and manage permissions, Send as permissions or Send on behalf of permissions.
- Select Add permissions, choose the colleague's name and select Add. Repeat for each permission type they need. Most people covering a mailbox need both Read and manage and Send as.
You can do the same in the Exchange admin centre at admin.exchange.microsoft.com: Recipients → Mailboxes → select the mailbox → Delegation tab.
Opening the mailbox you've been given
- Classic Outlook: mailboxes you have Read and manage access to usually appear in the folder pane on their own after Outlook restarts (this is called auto-mapping). Allow up to an hour.
- New Outlook and Outlook on the web: right-click Shared with me or Folders → Add shared folder or mailbox, type the address and select Add. In Outlook on the web you can also choose your profile picture → Open another mailbox.
- Sending from it: in a new message, show the From field (Options → Show From, or From in classic Outlook) and pick the address.
- Mac and mobile: Outlook for Mac shows auto-mapped mailboxes; in the mobile app use Add account → Add a shared mailbox.
Troubleshooting
"You don't have permission to send on behalf of this user"
The person has Read and manage access but not Send as or Send on behalf. Add the missing permission and allow up to an hour. In classic Outlook, delete the old address from the From drop-down autocomplete and select it again from the address book.
The mailbox doesn't appear in Outlook
Wait an hour, then restart Outlook. If it still doesn't show, add it manually as described above. Auto-mapping doesn't apply when permissions were given through a group.
Sent emails go to my own Sent Items instead of the shared mailbox's
That's the default. An administrator can change it with Exchange Online PowerShell (the MessageCopyForSentAsEnabled and MessageCopyForSendOnBehalfEnabled settings on the mailbox), so a copy is also saved in the mailbox you sent from.
Last reviewed: October 2026
