If you get a lot of emails or if you have an IMAP account you have maybe noticed that Mail gets slower and slower. The reason for the speed decrease is Mail’s Index file that grows with time. Deleting and moving mails causes gaps in that index file. To speed up Mail you just need to send that index file on diet.
(before you continue here make as usual a backup)
- Quit Mail
- Open Terminal ( Applications -> Utilities -> Terminal )
- Run command: sqlite3 ~/Library/Mail/Envelope\ Index vacuum index
- Optional: automate it on a weekly basis
Now your Mail should be fast again.