You can uncomment these lines to get more SMTP debug info:
https://github.com/salesagility/SuiteCRM/blob/v7.10.4/include/SugarPHPMailer.php#L446
https://github.com/salesagility/SuiteCRM/blob/v7.10.4/include/SugarPHPMailer.php#L486-L493
This will be helpful to see why the GSuite server is complaining.