EWS creates appointment with a default \"When\" text in the body. Please see the image below:
I created test appointments using EWS in the same manor above and explored the properties of the objects using MFCMAPI and EWS Editor. Via MAPI the when-text is stored in the PidTagHtml
property. Via EWS the when-text is stored in the Body
property. The when-text exists on the received copy, but not on the original in the sender's calendar folder.
Based on this it appears the when-text is inserted to the body at send time. If you remove the line
newAppointment.RequiredAttendees.Add("first.last@acme.com");
then an appointment is created instead of a meeting. In that case the when-text doesn't come into play.