if you wont to block anyone or remove youre own messages.
for blocking. click on the senders message and goto pull down menu MESSAGE and click on block sender and say yes.
to remove youre posts click on youre message to highlite goto pull down menu message and click on cancel message and then got pull down menu tools fined options click and fined maintenance click it you will see clean up now button click that and click remove messages and click yes. youre message no longer on server.