When clasiffying an e-mail to a particular workspace, i found it would be useful if the response you write could be classified to the same space too.
Also, i think it would be great if you could just have an option to auto-classify an e-mail depending on the workspace you are standing on by the moment you write it. Maybe also find a way to auto-classify the recepient's response?
It's just too painful to classify every single e-mail you write or receibe by hand, though this feature is great and really helps me organise my information for a given project