I realize this is old but I just went through this today and couldn’t figure out why my SMTP setup was not working correctly. So this is for anyone else that may come across the same issue, you can use Gmail smtp, you just have to generate an App Password as Gmail no longer supports what they consider “less secure apps”.
To generate an app password you have to login to your Google Account then find the “Manage Your Google Account” button. From there navigate to Security and find the heading “Signing in To Google”
You can then click on the App Passwords tab and follow the instructions to generate it. That password is then used on the Networking > Email Settings < tab or in the Alarming > Notification < tab to allow sending emails from an email address.
If you use the Email Settings option you can easily test your SMTP setup by using the More dropdown and clicking test and entering the same email address you used to setup the SMTP as the From address. You will know it works if you get what is inside the green box, any other message means it failed.
