In order to send a meeting request on behalf of someone else, you first have to have that person give you delegate access.
To give someone delegate access:
1. Open Outlook on the computer of the person who wishes to delegate their calendar.
2. Select File from the Outlook menu.
3. Select Account Settings and choose Delegate Access.
4.Select Add and choose the person to whom the calendar will be delegated from the address book. Select Add again and choose OK.
5. Accept the default permission settings in the Delegate Permissions dialog box. By default, the delegate can read, create, and modify calendar items.
To use your access to send a request:
1. Select Open a Shared Calendar and open the delegated calendar
2. Click New Meeting in the new group on the Home tab. Enter the meeting attendees, location, and start and end times as you would do on your own calendar.
3. Select Send once the meeting request is completed. You have just sent a calendar entry on another person's behalf.