The list of received messages does not give you any information of which ones have been replied. We think that it will be very useful to the users to mark those messages that have been already replied. Our plan is to add an extra column to Messages and use an icon to show if a message has been replied or not.
Right now, a user has to to keep track on their minds or check the "Sent" folder to see which messages have been replied. We have had several requests for this feature.
Please, see image attached.