So if somebody wanted to mail anthrax to, say, a government office, how would this stop that? Dropping off a stamped envelope in a mailbox in a different neighb

So if somebody wanted to mail anthrax to, say, a government office, how would this stop that? Dropping off a stamped envelope in a mailbox in a different neighborhood with no witnesses is not likely to get intercepted. And of course government efforts in "The War on Terror" would never be abused, right?