For most of our system, we have this feature called Email Alerts where it sends you notification via email informing you depending on the option you chose. Most of the time, this is used on motion detection events for you to be informed that a camera just detected a movement.
The setup is quite easy but some may encounter getting a failed test email considering that all of your settings are correct on your unit. One of the possible reason why is because Less Secure Apps setting of your Gmail account is turned on. Turning it off is like allowing devices like the recorder to use the email and send alerts to the recipient.
To know how this is done, please check Email Alerts: Gmail account setting (Less Secure Apps)