mail quits unexpectedly
mail keeps quitting unexpectedly
iMac 21.5", macOS 10.12
mail keeps quitting unexpectedly
iMac 21.5", macOS 10.12
And if John's great help isn't enough...
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.
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.
mail quits unexpectedly