Would be nice to have option to file and message in the inbox and it's reply with a related thread located in another folder.

Example:
20 messages in a thread have all been filed in folder XXX, A new message arrives in the inbox which is a continuation of that same thread. Clicking replay presents user with option to file the message with thread after sending reply (and also file sent message). Click send and the message in the inbox and the reply you just sent are both filed in folder XXX with the rest of the thread.