gistfile1.php

   <? // request the array of UID and criteria information
    $users = get_user_entities(get_users());

    foreach ($users as $user) {
      dpm($user);
      foreach ($user->collections as $collection) {

        // we only check to see if it's been set by the user and doesn't match,
        // so we catch matches and unsets if no continues are met in the ifs
        if (isset($collection->field_listing_type[LANGUAGE_NONE][0]['value'] && $collection->field_listing_type[LANGUAGE_NONE][0]['value'] !== $listing['type']) {
          continue;
        }
        //2nd if
        //3rd if
        //4th if

        //queue email to this user
        dpm($collection);
      }
    }