What's disturbing is this is common sense, NOT rocket science. Could a taped letter leak? It's a no-brainer to test. Put talc into an envelope, tape it up, check if it leaks even a tiny bit with handling. But, had the experts thought, such testing was unnecessary.
Could spores a thousandth of a centimeter across leak, contaminating the delivery route? Certainly. Even taped letters aren't airtight. Plus, they get handled in ways that might cause them to spill. They're jumbled in mailboxes, mailbags and sorting facilities. Most letters, including these, are machine-processed. Like packets of ketchup run over by a car, they zip through stamping and reading machines. Might imperfectly sealed envelopes puff out powdered contents if lightly and quickly squeezed along their length? Obviously. Imagining such unpleasant possibilities doesn't require Hollywood screenwriting.
Identifying delivery route contamination hot spots might be difficult, but it first needs to be thought of. Perhaps duplicate, labeled envelopes with identifiable or traceable powder of similar particle size could be tracked along the routes, with testing for spillage.
Sadly, experts in charge missed all this, even though that's their job and specialty. Were they impaired by lack of funding? Such thinking is free; solutions are expensive. It's troubling they were dull enough to not think this through. It's worrying that this might represent "expertise" on which we base security from bioterrorism. Worst of all, it cost several postal workers their lives, and ignored the larger, if lower-grade, risk to the public at large. The surgeon general's comment, "We were wrong," is their most accurate explanation to date.
Wash our hands, indeed.