macOS Sierra: Apple Mail Continues to Have Severe Performance Issues, plus crashes

Apple Mail in macOS Sierra:
pegs CPU for 30 seconds or so

See macOS Sierra: Severe Apple Mail Performance Problems; these issues remain a time-wasting headache every day, and have no solution other than waiting for the incompetents at Apple to issue an OS X update that fixes them. Hope for improvement is a foold’s game in MPG’s view, but not imposssible, so waiting until OS X 10.12.1 is my plan, since I’ve been traveling and will travel again soon, and switching mail clients is a Big Deal what with all the emails I have.

I’ve done all the suggested fixes in the above linked blog post, to no avail.

Apple Mail also crashes regularly, though not frequently.

Apple Mail in macOS Sierra: crashes not too often, but regularly