This article explains how to give someone the ability to send "on behalf of" you while preventing them from having access to view your inbox. You may setup Delegate access if you wish to grant someone the ability to both "send on behalf of" your self and view your email.
Click on the heading below for the mail client you're using. This will expand to display instructions specific to that email client on how to setup and grant permissions for sending on behalf of yourself.
Outlook for Windows
- Right click on your Inbox inside of Outlook (Usually on the far left side of the screen)
- Click Properties
- Click on the Permissions tab at the top
- Click on the Add button
- Search for and select the person to give permissions to, then click Add and OK
- Select the person you just added by clicking on their name in the list of those who have permissions to your inbox
- In the Permission Level: section, change the Write section to Create items
This will allow someone to send an email on your behalf, but will not allow them to view your inbox to read items. To setup the ability for someone to view and manage your inbox and send on your behalf look up "Adding Delegates in Outlook" to set that up all at once.
- Click OK
- This user can now Send on behalf of you. They can learn how to set their from address here
Outlook for Mac
Outlook on the Web (OWA, or office.com)