This is new to me (about the glue). How can the glue not have gotten contaminated if the envelopes were porous enough to let spores through? Wouldn't some spores have gotten on the glue that way?
Also, how would they have put the spores in the envelopes and then sealed them, without disturbing the spores enough for some to bounce and get stuck on the glue? (These are the same uncharged spores that fly easily and don't clump.)
Maybe the spores were placed in the envelopes while still inside some other sealed container? The envelopes would then be sealed, and the inner container would then be destroyed from outside, or maybe the inner container was made of a material that disintegrated. (This is a bit too much like Maxwell Smart, but it could be done.)
Do you suppose they had a lab built somewhere out in the forest?
I'm not convinced that it takes a complex lab to fill envelopes, or to put sealed containers inside envelopes. Certainly the requirements are much less than what's needed to prepare the anthrax spores in the first place.
And there are vast open spaces in the U.S. Mohamed Atta did a lot of traveling in Summer, 2001, for some unknown purpose.
Notice that, after the envelopes were opened, the subsequent contamination was limited. Only a small number of people were infected in a building, and adjacent buildings were not affected at all. (There appear to be only two exceptions to this -- Kathy Nguyen and Ottilie Lundgren.) If the envelopes were filled while on, say, a 50-acre tract, there would be no obvious contamination even if the terrorists had been a bit sloppy.
I'm an engineer not a chemist/drugest so I cannot comment on the effects or properties of the anthrax spores.
But, suppose the anthrax was prepared and stored in sealed hypodermic needles in a labratory environment.
The anthraxonist could address and seal an envelope and then inject the powder just before placing in the mail box. This could be done along one of the seams of the envelope without leaving much evidence and allow a semi sterile procedure.
Just a guess.