Go to AdminCP : Founder --> Mail Settings --> Settings --> Tick on the option: Send via SOCKET connection to SMTP server (supports ESMTP authentication)
SMTP password:
** this value was changed since May 30th, 2022. You need to create an app password via url : https://myaccount.google.com/u/0/apppasswords . Go ahead and create a name for app password. Copy the 16 characters length passkey . That's all, save it and check the result.