Mail crashing. macOS Monterey

Having similar problems. I handle both my iCloud mail (apple id) and my employer mail (Exchange server) using the Apple mail client. I thought at first I was having an exchange issue (that happens frequently) but this time Exchange is blameless. If I turn off my iCloud email in system preferences, the mail client works just fine handling my Exchange mail. If I turn off my employer email in system preferences and leave iCloud on, Mail crashes and locks up just about every time.

In the situation of iCloud email 'on' and all other email 'off', the Mail client appears to work properly for a few minutes and then either locks up or crashes. But even while working 'properly', a sent email will hang up and not go out. That's your clue that Mail just died. Also, if you try to quit Mail won't do so, and you have to force-quit. If you then restart many of the changes you made in the prior session didn't stick (moving an email to a folder, deleting an email, etc.).

I'm having this problem on all 3 Macs that I own -- an iMac 2019 Intel running Monterey 12.1, a MacBook Pro 2019 Intel running Monterey 12.0.1, and an iMac 2021 M1 running Monterey 12.0.1. I have iCloud active on all of them, but interestingly, when I connect to my iCloud mail on the web server, all is good.

I've tried deleting the 'envelope' files in the V9 folder within the library/mail folder, deleting the proper file in the Containers folder, and the plist file in the Preferences folder, and restarting. Didn't work.

I strongly suspect a memory leak.

Have you tried a restart?

Oh, and one more thing: my iPhone and iPad mail client is working properly for both iCloud and Exchange mail. Not a single problem.