Elementor-validate-form.php

<?php
/**
 * Check if a select field used for selecting differend recipients from the form match the allowed destination domain
 * Prevention of spam abuse of the form with publickly visible / manipulable destination address (eg. via browser developer tools) 
 */

add_action( 'elementor_pro/forms/validation/select', function( $field, $record, $ajax_handler ) {

        $allowed_form_name = "xxx"; // your Elementor form name
        $allowed_domain = "example.com";
        $field_id = "yyy"; // your select field id , eg. if shortcode is [field id="email-to"], then $field_id = "email-to"
        $form_name = $record->get_form_settings( 'form_name' );
        
        //validate only right field and right form
        if($field['id'] != $field_id || $allowed_form_name != $form_name){
            return;
        }
        if(!filter_var($field['value'], FILTER_VALIDATE_EMAIL) || substr($field['value'], strlen($allowed_domain)*-1) != $allowed_domain){
            
                $ajax_handler->add_error( $field['id'], 'ERROR: wrong or not allowed email address' );
            
        }
 }, 10, 3 );