We need a group of people to be able to schedule other people to use several resources (such as on equipment calendars) when they forget to schedule themselves.

There used to be a "Invite Attendees" icon in the Outlook 2010 ribbon and we could click the button and schedule other people on the resource so that it the booking doesn't get added to our personal calendars.

What are the minimum required permissions to make this work?  I have tried using the EMC to add a security group as delegate, but the "invite attendees" icon doesn't appear.  Does everyone really need to have full control of the mailbox to make the icon show in Outlook or does the icon needed to be added to the ribbon manually for each person?