you probably clicked "send replies to my inbox" button. its located by the first post of a board. it has a envolope next to it. when you click it all the replies go to your inbox. to stop it just click it again
omg that happened to me too!! I asked my bro urgently what is happening like 3 months ago and he just made it so they couldnt see my email anymore so since they dont know my email they cant send anything to me. but you might have accidently also pressed to send messages to outbox button!