Starting from July 15, 2019, Google are changing the way that third party apps are allowed to make use of their Gmail API. While this change primarily affects the way in which apps can access Gmail data, it might also affect the ability for third party apps to send gmails.
For more details on this change read this.
If you are using a Gmail account to send emails from RightBooth, then as a precaution we recommend that you have another email account ready to switch to should Google block third party app emailing.
For example, you can create a free outlook email account at https://outlook.live.com. Then in RightBooth Social media settings, set the Email server as follows: