on sierra mac mail opens with white page
When I open mail the message is a white page. consistently across all email regardless of who sent or what content. Happens every time! appears to be Mac OS Sierra bug.
macOS Sierra (10.12)
Does this happen if you boot in safe mode? See - Try safe mode if your Mac doesn't finish starting up - Apple Support even though your Mac starts up ok.
Does this happen if you create a new user account and use that? See - OS X El Capitan: Set up users on your Mac