Here's the "Circle of Life" with Exchange syncing in rich, artistic, diagram form. You'll notice there are two types of connections made:
Robin syncs with Exchange using a service account. You can think of the service account like our "key" that we use to fetch and save updates made in Robin back to your calendars in Exchange. These updates are "Inbound" connections to your network that Robin initiates.
When Robin first connects to a calendar in your Exchange server, it "subscribes" to receive notifications whenever the calendar's schedule changes. This means Robin doesn't have to constantly ask your Exchange server "Hey, is anything new?" to keep up to date. Instead, Exchange can let Robin know whenever something happens to one of those channels and Robin will update its version of the event as well. This approach is faster and lightweight for everyone involved. These updates are "Outbound" from your network, because they are not initiated by an outside request.
Some network configurations will block these types of connections by default. If you discover changes made in Outlook aren't syncing back to Robin, make sure your network allows Exchange to let Robin know when changes happen.