I just came across this email, and it's just too delicious not to share.
Thank you for publishing your titles on the Kindle Store through Amazon DTP. During a review of your titles, we noticed that you used Calibre to create Mobi books. Please note that if you use Calibre to create Mobi books, they may not be supported if we add features to the Mobi format. Therefore, we suggest that you use applications like KindleGen or Mobipocket Creator instead.
KindleGen is a command-line tool used to build eBooks. This tool is best for publishers and individuals who are familiar with HTML and want to convert their HTML, XHTML, XML (OPF/IDPF format), or ePub source into a Kindle Book. Please click the following link to download this application along with the User Instructions:
You can also find more information and instructions for using the KindleGen in our Kindle Publishing Guidelines document. Please click the below link to download the same:
However, if you would want an application with an active User Interface, you can use Mobipocket Creator. The Mobipocket Creator allows publishers to create ebooks with an easy-to-use content authoring tool. This software also includes Adobe PDF, Microsoft Word & Text File Import wizards. You would also be able to design an active Table of Contents and a personalized cover image for your titles.
Please note, KindleGen does not support DRM. If you want to apply DRM to your books, you can do that through the DTP web site.
If you have any questions, please feel free to write to us at [email protected].