in a communication tree, soon there is a collection of messages -re --re re --- re re re etc. If I answer a single email and my mail starts with re: subject, it is immediately noted as 'already replied to' after sending. Doesn't wait for actual replies to come in. Win 7, newest TB.
For messages without re: very convinient addon
This review is for a previous version of the add-on (0.6).