In answer to some of your questions, I'm running Windows 7 on my PC and I have a Kindle Fire (not HD.) I don't know which model, got it for xmas 2 years ago, if that helps.
I have my newsfeed set up to email to
myname@kindle.com, which is what is displayed on the top of my "documents" page. The feed is is set to send in MOBI format. Calibre says it's sent, but then I cannot find it on the kindle. It's not in the documents file. I've sent myself pictures in the past to that folder, so I am mystified as to what may be going on. I can't find any answer on the Calibre website or FAQs.
I'd really like to be able to use this feature!