This isn't just a Leanpub thing. Here's a link from the Microsoft Press Pearson store which explains why they stopped providing MOBI on August 18, 2022:
This is the exact reasoning that we used when we discontinued our MOBI support.
Amazon's Send to Kindle app is the easiest way to send files to your Kindle. However, it may or may not support EPUB in your region. Chances are it will by the time you read this article.
However, if Amazon's Send to Kindle app doesn't support EPUB in your region, it is actually supported through the Kindle Personal Documents Service.
It's in the list of supported files in the Kindle Personal Documents Service on Amazon's help page here:
So, you can already add an EPUB to Kindle by sending it as an attachment in an email to your Send to Kindle email address.
More conveniently though, you can add your Send to Kindle email address to your Leanpub account here:
When you select a Leanpub book in your library, if there's an EPUB version, you can then just click the Send to Kindle link:
That feature used to send the MOBI version; now it sends the EPUB version.
If you were downloading MOBI files and transferring them manually to your Kindle device, you should be able to do the same thing with the EPUB version.
If the EPUB file is too big to use the Send to Kindle feature, please see this article.
If you encounter any issues with this feature, or if something has changed and we should update this article, please let us know by contacting the team at email@example.com!
OK, that's it!
If you have any feedback or questions about this article, please email the Leanpub team about it at firstname.lastname@example.org!
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Interested in creating your first Leanpub book? Here are some quick tutorials for our most popular writing modes: http://help.leanpub.com/en/articles/3088382-quick-walkthroughs-for-getting-started-on-a-leanpub-book