my mail application will spontaneously close; I cannot determine why

Hi sleep dog,

Thanks for using Apple Support Communities. We understand the Mail app is unexpectedly closing, and we would like to help. Check out the steps to take when an app unexpectedly closes here:

1. Quit and reopen the app

Quit the app, then open it again. If the app won't quit, force the app to quit. Then check to see if the problem with the app is fixed.

2. Restart your Mac

Restart your Mac. Then check to see if the problem with the app is fixed.

3. Check for updates

To see if updates are available for the app, open the App Store, then click Updates. If updates aren't available for the app, update the software on your Mac. Or if you didn't get the app from the App Store, look for updates to the app on the app developer's website. Then check to see if the problem with the app is fixed.

4. Reinstall the app

Delete the app. When you do this, you might lose data that was stored in the app. Then redownload the app. If you didn't get the app from the App Store, redownload the app on the app developer's website. Then check to see if the problem with the app is fixed.

See more about those steps here: If an app on your Mac stops responding, closes unexpectedly, or won’t open - Apple Support

Thanks.