Fixed my slow loading mail.app
Have you seen mail take 1-2+ minutes to start? I have. Spent more than an hour with tech rep without solution. Final step she suggested: reload new macOS. I was running the latest version of Monterey 12.2.1; This problem only showed up on my main imac, not by 2012 macbook air or mac mini. I did the "reinstall macOS from the recovery bootup". Mail slow load fixed! Started in less than 3 seconds, when it was 3 minutes an hour ago before the reinstall.
iMac 27″ 5K, macOS 12.2