3.1.4.10 Setting Message Object Read State
A client marks one or more Message objects as read or unread without opening the Message objects by sending a RopSetReadFlags ROP request ([MS-OXCROPS] section 2.2.6.10).
When a user marks or unmarks a single opened Message object as read, the client sends a RopSetMessageReadFlag ROP request ([MS-OXCROPS] section 2.2.6.11).