Great source! That is a self-typed copy of the presumed letter.
Since you and O-S seem to get along much better than I have been able to do with him, could you please ask him to post the actual letter to his website, as he was so willing to do with the C&D letter? That would help prove its authenticity.
I in turn can then take a copy of that letter from the site to AT to confirm they did in fact generate it..... I'm sure the local branch here has probably sent several out on what appears to be a form letter to concerned clients, and can provide me one as well.
See, no claims by me of the letter being a fraud. Just a mutual respect of both of us in doing DD, and trying to get confirmation on this serious matter.