Mail using 80-120% of CPU?!

I've been having trouble with Mail app freezing up (Monterey 12.3.6) and discovered it was using over 100% of CPU. I've disabled all email accounts in the preferences. Restarted the computer. Opened Mail--with no accounts enabled--and it's still using 70-80% of CPU. Activity window inside of Mail does not show that it's doing anything. As I reenabled accounts, CPU usage goes back to 100 % for mail--or more--and the application hangs (won't send, won't delete/move messages, requires force quit).