Originally Posted by Blossom
All emailed books will be under docs. The email address for the Fire is for Personal Documents only. You have to sideload via USB to get books to show up under Books. Just drop your books in the books or documents folder. It doesn't matter which. They must not have a pdoc tag on them or they will show up under Documents instead of Books.
I highly recommended you read the stickys here and search the threads. This has been answer numerous times. Do a search for the word ebok and that should get you the threads that will help you.
Actually, the statement in bold is incorrect. As posted here previously, I have always converted my mobi books via Calibre with a [PDOC] tag and they always appear on the BOOKS bookshelf when side-loaded.