- Browse to the site or site collection where you created the site mailbox.
- Click the gear icon for the Settings menu, and then click Site settings.
- Click Site permissions.
- On the ribbon, click Grant Permissions.
- Click SHOW OPTIONS, select the Members or Owners group permission level, enter the name of the affected user, and then click Share.
For more information, go to the following Microsoft website:
Article ID: 3069134 - Last Review: Dec 21, 2016 - Revision: 1