MyMailbox.scala

import akka.actor.{ActorRef, ActorSystem}
import akka.dispatch.{Envelope, MailboxType, MessageQueue, ProducesMessageQueue}

class MyMailbox extends MailboxType with ProducesMessageQueue[MyMailbox.MyMessageQueue] {

  def create(owner: Option[ActorRef], system: Option[ActorSystem]): MessageQueue = ???

}

object MyMailbox {

  trait MyMessageQueueSemantics

  class MyMessageQueue extends MessageQueue with MyMessageQueueSemantics {

    def enqueue(receiver: ActorRef, handle: Envelope): Unit = ???

    def dequeue(): Envelope = ???

    def hasMessages(): Boolean = ???

    def numberOfMessages(): Int = ???

    def cleanUp(owner: ActorRef, deadLetters: MessageQueue) = ???

  }

}