After installing, enabling and configuring Drupal's PHPMailer module using Google gmail SMTP server, still could not send out email.
- Login to gmail, authenticate again with mobile phone received code from google.
- Click Display Unlock Captcha to "Allow a new application to access your account.
- When configuring the PHPmailer module, there is a useful Debug level selection and Test Configuration. Try these and will find out the issue was caused by Gmail authentication problem.
- Google is so smart that they are aware of your mail account being used by an application such that they would block your account immediately to mitigate risk of being hacked, and let user to do some more step for re-activating the account, and further acknowledge the use of application to send out email instead of a proper email client.