Since keeping message as unread is far from optimal way to keep track of important emails and so is checking 'sent' folder for reviewing communication, you can use simple RTM to help in two ways:
1) (obvious) Setting todo task for received email message that you need to reply
2) Creating task for sent email right after sending it.
This will create "email channels" (e.g. as separate list) that provides quick review for communication (similar to way routers work)
P.S.: You will understand full potential of creating list for sent messages when you communicate with people who use internet on low-frequency basis (Like someone's grandma said: "Do email get delivered on ?")
Posted at 5:49pm on October 10, 2012