Start with this of M1 or M2 Mac...
On your Mac, choose Apple menu > Shut Down.
Wait for your Mac to shut down completely. A Mac is completely shut down when the screen is black and any lights (including in the Touch Bar) are off.
Press and hold the power button on your Mac until “Loading startup options” appears.
Select a volume.
Press and hold the Shift key, then click Continue in Safe Mode.
The computer restarts automatically. When the login window appears, you should see “Safe Boot” in the menu bar.
Restart normally.
Start with this if IntelMac...
Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes or more.
Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, 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.