I appreciate Hiri's approach to handling e-mail but a folder structure is still of great value for some workflows. For example, in some instances other people may have to go through my e-mail on my behalf and being able to look in certain folders is essential. I miss two facilities that are critical to my work flow:
(i) Saving a reply in the folder in which the original e-mail has been copied.
(ii) Keystrokes to facilitate common tasks. For the latter, the Nostalgy plugin works well on Thunderbird and illustrates what is required. The essential keystrokes for me are: Move an e-mail to a folder, Move an e-mail to a folder and go to that folder, Go to a folder.