Wrote this piece on SmokingApples.com.
For screenshots and comments, go to the original postEveryone who has used Gmail has found the conversations feature to be one of the best ways to browse through the hundreds of emails that come through everyday. Moving to a desktop client, on the other hand, presents email in the old school way, one after the other.
Except for Mail. By default, Apples Mail client will colour any similar emails light blue, when any one of those messages is selected. A little known extension to this feature is that there is a threaded conversations view (View > Organise by thread). This will group similar messages into a single thread, much in the same way as Gmail does it. And all this is done use some super slick animation effects! However, unlike Gmail, it excludes any messages that you have sent in that threaded group.
But thats not the end of it. Since each reply is marked and linked to any message, clicking on that button (screenshot 3) will bring up your reply in a new window.
A little warning though: Threading your emails might make the blue tint, now all over, a little overwhelming. Just open up the Mail Preferences (Command+,) and in the viewing tab you will be able to change the colour using the default Apple Color Palette. Changing the colour to a light shade of blue, as seen in the screenshots, is much easier on the eyes.
(Note: Those emails you see in the screenshot were for that purpose only. I dont usually flood my inbox with self praises.)