Woocommerce : How to automatically input the same email for every order?

In order to achive that you only need two woocommerce filters.

First we remove the email post field from the checkout form.

Second we set the the submited form data, email, to some fixed value.

This is the whole code, paste it into functions.php and you are good to go. Don’t forget to change the email to what ever you need.

add_filter('woocommerce_checkout_fields', 'bt_manipulate_checkout_fields');
function bt_manipulate_checkout_fields ($fields) {
    unset($fields['billing']['billing_email']);

    return $fields;
}

add_filter('woocommerce_checkout_posted_data', 'bt_manipulate_checkout_posted_data');
function bt_manipulate_checkout_posted_data ($data) {
    $data['billing_email'] = '[email protected]';

    return $data;
}