All of a sudden yesterday my outlook will not longer sync to my Google account. When I try to send an email I get the following error message. I was on with support for three hours and they eventually said they couldn't fix it.
This particular error would suggest that Google has blocked the account for potentially malicious activity, so they would be the ones to resolve this particular error. Are you able to send from the gmail website? You may also want to check the activity on your account and change your password.