Add this snippet to your functions.php file or use the Code Snippets plugin:

add_shortcode('users-email-domain',extract_domain_func);
function extract_domain_func(){
   $current_user = wp_get_current_user();
   $email = $current_user->user_email;
   if( filter_var( $email, FILTER_VALIDATE_EMAIL ) ) {
      // split on @ and return last value of array (the domain)
     $domain = array_pop(explode('@', $email));
     return $domain;
   }
}

Usage [users-email-domain]