as describbed on http://social.technet.microsoft.com/wiki/contents/articles/1151.exchange-activesync-overview.aspx (chapter: Exchange ActiveSync 14.0)
since Exchange 2010 (EWS v14) there are available message attributes like the reply state.
This way multiple clients cannot only se the read-state of messages in the mailbox but also know if the message was already answered or forwarded. (Outlook shows a symbol beside the message)
My question is if this attributes will be supported in future Smartermail EWS-Versions as customers are asking for it.