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

Delegation gives Office 365 users permission to access certain features of your mailbox, such as:

• Viewing and/or making appointments on your calendar.
• Looking at and updating tasks.
• Reading mail in your inbox and sending mail on your behalf.

If you have access to another's account and act on their behalf, you are known as a delegate. If the other person does not need to be a delegate, you can use conventional sharing (see Sharing your Calendar and Sharing mailbox folders) to grant them a more limited form of access.

If you use Outlook 2010/2013 (Windows):

http://office.microsoft.com/en-us/outlook-help/allow-someone-else-to-manage-your-mail-and-calendar-HA010355554.aspx#_Toc257793592

If you use Outlook 2011 (Mac):

http://office.microsoft.com/en-us/mac-outlook-help/add-and-manage-your-delegates-HA102928247.aspx?CTT=5&origin=HA102928235