HI,
Check by enabling 2-step verification in Gmail and then assign the app its own application password, instead off your regular password. Try signing into the mail app again.
And also make sure to check SSL checkbox 465 port.
Did you see the link to the help page in your exception listing?
https://support.google.com/mail/answer/7126229?p=BadCredentials&visit_id=637600495381370008-4276557114&rd=2#cantsignin&zippy=%2Ci-cant-sign-in-to-my-email-client
These the suggested steps you need to take…
Step 1: Check your password
If you have these problems or can’t sign in, first check to make sure you’re using the right password.
Step 2: Try these troubleshooting steps
Hope this helps