There is References element in Exchange. It represents an array of ids of messages which are referenced by a message. I have been wondering if the order of the ids in this array is specified (and if yes then what specifies the order) or the ids come in a random order. Thanks
References is the RFC references header from a Message which is defined in https://www.rfc-editor.org/rfc/rfc4021#section-3.6.4 . The order of the Id's isn't defined in the rfc so its open to interpenetration by any mail agent. In 99% of cases you'll find that are they are just appended by each mail agent but it not 100% because the rfc doesn't define it to be that way. EWS just reads an return whats in the underlying header so is no different from any other Mail server.