I think GMAIL enforces 2FA now… in any case, once your logged into Google account, manage account > Security > Signing in with Google and go to App Passwords.
Generate the app password using the device and app dropdowns… choose Mail as APP and descriptive device so you know what it is if ever you need to delete.
When you generate, it’ll show a password… which you will use in the Peplink email notification smtp password. You can’t recover this password later, so copy it into the peplink smtp password textbox, or copy it temporarily somewhere.
here is my config:
SMTP username is the first part of your gmail before the @ symbol.