If one controls the mail, they can change what is written an what is given to someone else. The one who controls the mail can toss a package or a letter out and just say that it was lost. The one in control of the mail has the ability to either send, keep, or toss out items. If the one in control of the mail does not want information to get somewhere, all they have to do is toss the letter or package and just say that they never revieced it or just say that it was lost in transit or while sorting.
Newman = KKK. That line is a reference to a sinister threat that Newman made to Jerry because Jerry refused to give into Newman's BS. Newman is a KKK man at heart. He is a thug and an a--hole. He has no warmth in his heart. He is a cold arrogant douche.
Although all the information is censor and filtered by the sender, other messages can be found by other alternatives. For example, the message about tobacco is overall negative. Still, people still use these products. They still have the choice to find alternative ways to receive positive reasons to continue a behavior or looking for other alternatives.