You are using Microsoft Outlook 2013 Service Pack 1 (SP1) or a later version.
You are connected to a Microsoft Exchange Server 2013 Service Pack 1 (SP1) or Microsoft Exchange Server 2016 mailbox.
The Exchange mailbox and Client Access (CAS) servers that you are connecting to all have Exchange Server 2013 SP1 or a later version installed or Microsoft Exchange Server 2016.
The necessary server settings to establish MapiHttp connections are correctly configured.
In the above scenario, the Protocol column in the Outlook Connection Status dialog shows Outlook 2013 is connected to the Exchange server using a connection mechanism other than MAPI/HTTP. For example, the following figure shows a connection using RPC/HTTP.
Note MAPI/HTTP connections are designated in the Protocol column using the string HTTP.
This problem can occur if the MapiHttp feature is disabled on the Outlook client using the following registry value: