My mail keeps crashing on my Mac

Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

If still no good Disconnect from the Internet, then start Mail, look for the last rec'd eMail.

Does Mail crash if no internet?

Quit Mail & login to your WebMail in a Browser, if possible delete any later eMails there after the last rec'd one on the Mac.

If you have no POP accounts & they’re all IMAP accounts then in Mail’s Mailbox menu choose Rebuild.

I have the same issue, although it isn't a huge problem -- just thought I would report in. I can be working on something else in another program, when mail suddenly crashes for no reason -- it's open, but I'm not checking my mail. Strange to have it crash when open, but not being used. It has happened several times in the last two weeks.

I had the same problem. I turned off Wi-Fi before opening mail and no crashing. If that works, then turn on your Wi-Fi and quickly select "Take All Accounts Offline" from the menu in Mail. Hopefully still no crashing. Then from the menu in Mail, one by one bring each of your mail accounts back online waiting to see if one of them crashes. In my case Mail didn't crash, but one account no longer showed any messages. If that happens or you get a crash, repeat the process from turning off your Wi-Fi but instead of bringing the accounts back online, create a new account in Mail using credentials from the problematic email account and then delete the old one. You should then be able to bring all accounts online. This worked for me. Hopefully it saves some of you from having to attempt more radical measures.

The problem seems to have corrected itself with the latest Big Sur updates to Version 11.3. Hopefully it will stay corrected!