The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required.
Go to you email account settings at https://myaccount.google.com/
Security settings required by G Suite.
- A strong password. I create a new strong password. Confirmed.
- 2-factor auth is off. Confirmed.
- Access to less secure apps is enabled. Here is screenshot of my settings, the first is the admin console enabling it for users, the second is the user enabling it: