the Unread property sets filtering on whether or not a message has been read. Read/write.
objMessageFilter.Unread
Boolean
A message's Unread property is True if it has not been read by the current user.
For more information and an example using the Unread property, see Filtering Messages in a Folder.
The Unread property corresponds to the MSGFLAG_READ flag not being set in the MAPI property PR_MESSAGE_FLAGS.