Why is Apple Calendar notifying me of an invitation to an event which is in someone else's email or calendar?

My company uses Google Apps for which I am a super admin. I personally use the web interface for email and calendar but have the accounts setup on my macbook and iphone so I can use Mail.app or Calendar.app. My colleagues mostly use Apple's Calendar on OSX and iPhone. Calendar.app on my laptop keeps notifying me when one of my colleagues has an invite in their email. It is really irritating and confusing to receive their invites. What is going on? and how do I fix it?