Note: Before proceeding, please review Best Practices for Sharing and Delegation – Office 365

You can choose to grant individuals access to specific mailbox items.

Outlook on Windows (2010/2013)

1. In the navigation pane, select the folder you want to share:
   

2. In the Folder tab, click Folder Permissions:
     

3. Click Add…:
     
4. Search for the person you want by name. Click the Add -> button, and press OK once you’re done adding users:
    
5. Customize their permissions for this folder by using the Permission Level drop-down menu and the checkboxes below:
   
    
6. Click OK once you’ve finished setting permissions.

Note: It is not recommended to share your entire mailbox. If you need to grant this level of access to someone, adding them as a delegate is the best option.

Outlook for Mac 2011

If you use Outlook for Mac 2011, please see the following guide: Share a Folder in an Exchange Account