Via Lifehacker: Bookmark Your Email with Gmail or Mail.app. Unfortuantely, I don’t use Gmail or Mail.app, the former because I don’t like being tied to specific vendors, and the latter because I can’t deal with its message threading. I’ve been searching for a way to do this with Thunderbird (my client of choice) for some time now. Maybe this will inspire some Thunderbird hacker to implement the functionality.
How does Thunderbird do mail threading differently?
Thunderbird collapses conversations under the first message in the thread, indenting each level. (Identical to the way Mutt does things.)
Mail.app does this weird quasi-index that displays a list of messages in the conversation with no indenting. If I recall correctly, it also uses the subject of the most recent message.