No, but it might be consistent with delivery via an envelope. The difference is not subtle. A "letter" goes through postal routes. An "envelope" might simply contain rent money inside it.
Anyway, I'm not claiming that the 9/11 terrorists put contaminated rent money inside an evenlope to give to their AMI landlord. What I am pointing out is that it is plausible for a tenant to put place rent money in an envelope, so if the required amount of anthrax contamination is so large that it demands delivery via envelope, you still can't rule out the rent money theory (well, *you* can rule it out, but that's only because you are wedded to an obsolete, different theory).
What I'm pointing out is that your arguments get more and more absurd with every posting.
You now fantasize or rationalize that there could have been an envelope because it would be ridiculous for all that powder to be on the money itself. Thus, you now argue that the money could have been in an envelope.
You're just making stuff up to explain away the evidence that your theory is absurd.
Question: Why would the money be carried into AMI in an envelope?
Answer: Because you need that to be true in order to explain away the undeniable fact that it couldn't have been on the money itself.
Money in an rent envelope isn't going to contaminate the mailroom. It isn't going to contaminate mail bags. It isn't going to contaminate the mail van. It isn't going to put spores into Stephanie Dailey's nostrils. It isn't going to put spores into Ernesto Blanco's nostrils. It isn't going to contaminate mail sorting slots. And it certainly isn't going to leave a trail from Trenton to Boca Raton (or vice versa).
Your attempts to rationalize ways your theory could still be true - in spite of the overwhelming evidence that it is total nonsense - are just getting more and more ridiculous.