[cybmole]

update: I could not resist a couple more test.
file sizes: I chose a book which converts to 3Mb with mobi: both, and to 800k with mobi: old. whichever I send, I only get the 800k file on Kindle Fire, so amazon are throwing away 2/3rd of the 3Mb email.
everything I tested with amazon email ends up in my KF documents folder with a gobbledygook actual file name but appears on the carousel & is listed as a document.
PS and the copies of the various emailed .mobi files which amazon helpfully also place in my cloud drive all have .azw extensions in the cloud !