] I'm not saying this is a genuine article, but I think the seller is misspeaking (miswriting?) when he calls it an envelope. He also calls it an envelope panel. It looks to have been cut out of a larger piece of paper, rather than an envelope as we know it.

Well, I tried to be delicate by not directly telling it was not real, Leif told it for me.

If it were cut of a piece of paper, the address on one side would not be more important than the content of the letter itself on the other side. I could believe it was real if there was the autograph since it's known JA's siblings cut her autographs from letters they received from her to give to her fans, but it's not so.