Make Apple Mail.app faster
(sources comments: [#1] and [#2]) It DOES work. For instance, check how many times Mail.app bounced on the Dock before opening before and after you did this operation. Might prove worthy of use for Yojimbo, too.
sqlite3 ~/Library/Mail/Envelope\ Index vacuum .exit
Shrink (a bit) winsxs
(source) Removes SP1 uninstall files.
dism /online /cleanup-image /spsuperseded