I've been doing some housekeeping with my ebook files. For years since the kindle first came out I have been selling .prc versions of my novels for kindle devices. I generated these ebooks out of Mobipocket Creator. Strangely this software generates .prc files but does not make .mobi files. I guess they are supposed to be the same thing, but after the Kindle Fire came out I got feedback that the .prc files did not want to sideload as they always had before with earlier Kindles. As far as I can tell, the ebooks with the .mobi file extension will work better across all Kindle devices.
The trick was how do I make .mobi files? I couldn't figure out how to make Mobipocket Creator do it, which seems odd. I found the Kindle Previewer and Kindlegen programs from Amazon, which seemed to be a perfect solution, but after reading the terms of service, I saw that I technically was not supposed to use files generated from these programs for commercial purposes outside of sending the files to Amazon.
Although I was doubtful I would ever be busted, I still try to avoid violating terms of service and went looking for another solution. I opted for the ever-popular ebook library management system of Calibre. This program converts numerous formats to numerous formats, including .mobi. I converted my .epub ebooks that I make with Sigil into .mobi through Calibre and everything worked out fine. I will admit that I tested all the files in Kindle Previewer to see how they rendered across all Kindle devices. Everything looked good, so now all the Kindle compatible files served from my site are .mobi and will hopefully work well for everyone involved.
By sharing these tedious details in the life of an author publisher, I hope that I might help some other web surfer find the ebook conversion information he or she is seeking.