} else if curIdx < sortedIdx {
					return fmt.Errorf("conflicting callback %s with before %s", c.name, c.after)
				}
			} else if idx := getRIndex(names, c.after); idx != -1 {
				// if after callback exists but haven't sorted
				// set after callback's before callback to current callback
				after := cs[idx]

				if after.before == "" {
					after.before = c.name
				}

				if err := sortCallback(after); err != nil {

			return nil
		}
		return err
	}

	if err = target.send(eventData); err != nil {
		return err
	}

	// Delete the event from store.
	return target.store.Del(key.Name)
}

// Save - saves the events to the store if queuestore is configured, which will
// be replayed when the mqtt connection is active.
func (target *MQTTTarget) Save(eventData event.Event) error {
	if target.store != nil {