Delegate Access in Outlook
Using Delegate Access, you can give someone permission to act on your behalf. For example, you might have an assistant that you want to create and respond to meeting requests for you. Some assistants might also monitor a manager's Inbox and send email on behalf his or her behalf.
How to Give a User Delegate Access
Open Outlook and click on the File tab

Click on Account Settings

Select Delegate Access

Click Add

Enter the name of the user that you would like to provide access to here. Then choose the arrow to search.
Choose the user from the list, press the add button in the lower left corner, and select OK.

A window will open and ask you to set permissions. Set all permission to None to only allow the user to send emails on your behalf.

How to Send Emails on Behalf Of Another User
Open Outlook and compose a new email. Click on the Options tab.

Click on From

Enter the full email address of the user that has provided you with delegate access and click OK. You should now be able to switch the "From" field by selecting the From box
