Apple Mail Crashes on startup

If Appleā€™s mail app crashes on startup, then force a rebuild of its database by removing this file and any other files with the same prefix :

/Users/<username>/Library/Mail/V2/MailData/Envelope Index

There may be multiple Envelope Index temp files present. This delete command will remove all of them.

rm -f ~/Library/Mail/V2/MailData/Envelope\ Index*