Do you really think postal workers will happily sort mail containing potential anthrax or even fake powder and then deliver it every day for the next 3 months without freaking out?
If we assume that CDC/FBI whoever decides white powder is a potential threat, they will figure out equipment, dogs, what have you to "sniff" every package, envelope, etc. at every postal collection station. If postal employees believe that there is a potential for antrax to be in the mail, they will demand to work in full body contamination suits to pick up the mail and sort it. I would expect nothing less of anyone.
OK, so we can say that if white powder envelopes are a threat, the internet email traffic will soon replace regular mail, which will grind to a halt. Therefore there will not be a need for massive use of antiboitics etc. The mail will not be delivered as you envision.
Sorry, but your theory doesn't pencil out by my way of thinking.
It seems the government, as would be expected, has always looked at "the big picture," and not this kind of psychological warfare. Consider also the loss of jobs (whatever you think of snailmail) if the postal service suddenly shut down, and the fact that packages can't be e-mailed.
I've been wondering myself how long it will be before there's a response from postal workers. Also, if all this stuff has been going through the mail, unless it's really well sealed in the envelopes, shouldn't there be some cases of anthrax among postal workers (even if most of the envelopes were "duds")?
If postal employees believe that there is a potential for antrax to be in the mail, they will demand to work in full body contamination suits to pick up the mail and sort it.
Working in full body suits (properly, anyway) is not all that simple, and not everyone can handle it physically or mentally.