from the desk of stinkpot

i found this over on hawk wings and it worked like a charm; my folders in apple mail now open about 50% faster than they did prior to this extremely straightforward hint:

1. Quit Mail.

2. Open Terminal.

3. Type the following:

cd ~/Library/Mail
sqlite3 Envelope\ Index

An sqlite> prompt will appear.

At that prompt, type vacuum subjects;.

After a short delay, the prompt will return. Type Control-D to exit.

4. Restart Mail and enjoy the extra speed.