SharePoint to Create OUTLOOK Calendar Events for All Users

Hi Team,

            Would you able to tell us what level of Security does a Service Account should have in order  SharePoint (2013) to Create OUTLOOK Calendar Events for All Users. We are trying to incorporate Staff Annual leave into SharePoint, so when a staff annual leave get approved  by their managers, staff OUTLOOK calendar get blocked out with the Calendar event saying "Annual Leave". But i could not get the AD service account to get perform this - insufficient permission

I have tried all of these built in roles so far with out any luck, any thought on this please?

We are running Exchange Server Version 2007 as well as 2013 (Bother are co exist together)

Thanks