OptionalbodyOptionalfromOptionalidOptionalsubjectOptionalthreadOptionalthreadIdentifier for the message thread, generally the ID of the sender's copy of the first message
OptionalthreadNumber of messages in this thread. Only included when threads=true
OptionaltoOptionaluserID of the user to whom this message belongs. Messages work like email, so the sender gets a copy and the recipient gets a copy of each message. This is always the authenticated user, so there's no real need for a full user object.
Array of flags on messages in this thread. Only included when threads=true