cx-newsletter/renders/scripts/smtp-chide.js

document.addEventListener("DOMContentLoaded", () => {
    const checkbox = document.querySelector(".custom-smtp-checkbox");
    const custom_smtp_form = document.querySelector(".custom-smtp-form");
    
    const visible_update = () => {
        if (checkbox.checked) {
            custom_smtp_form.style.display = "";
        } else {
            custom_smtp_form.style.display = "none";
        }
    };

    visible_update();
    checkbox.addEventListener("click", visible_update);
});