On MacWorld Joe Kissell provides a list of 34 software tweaks
that will speed up your Mac.
Mail.app gets a speed bump from reducing the size of your mailboxes, spring-cleaning the Previous Recipients list, reducing the frequency of mail-checks and by adjusting your IMAP settings.
iCal gets faster if you weed out old appointments and events.
You might also want to try rebuilding Mail.app’s database, which worked a treat for me.
Tags: Apple Mail, Apple Mail Tips, envelope index, iCal, imap, mail-check, mail.app, mailboxes, Previous Recipients