Mail quits unexpectedly

Hello Steamboat Cowboy,

Welcome to the Apple Support Communities. I understand your Mail app is quitting unexpectedly. Being able to use Mail is critical, and I'm glad to offer some troubleshooting steps.

For clarification, System Integrity Protection is a critical security function of your Mac and should be enabled: About System Integrity Protection on your Mac

Regarding Mail, does it quit as soon as you open it, or while it's in use? If it's during use, what actions are you taking when it quits?

If it quits immediately after launch, make sure the app is fully closed and then hold Shift while you open the Mail app from the Dock. This bypasses the saved state the app was last in, and might help.

If that doesn't help, boot into safe mode to see if the issue occurs there. This will help rule out a few software causes: How to use safe mode on your Mac

Feel free to reply back with how it goes in safe mode.

Have a great day.