Are you a .Net Developer who develop custom application using Exchange Web Services (EWS) Managed API or EWS (Auto-generated proxies)? Then this is for you. The EWS Managed API provides an intuitive interface for developing client applications that use EWS. The API enables unified access to Exchange resources, while using Outlook–compatible business logic. In short, you can use the EWS Managed API to access EWS in versions of Exchange starting with Exchange Server 2007 Service Pack 1 (SP1), including Exchange Online. However, do you know that not all features that are available in EWS are implemented in the EWS Managed API?
You can refer the above snapshot or related documentation identifies the EWS Managed API feature implementations that target different versions of Exchange. If the EWS Managed API does not implement a feature that you want to use, you might consider an auto-generated proxy object model.