Amazon had blocked AZW3 files/books from alternate sources and allowed mobi files to be downloaded to our newer Kindle Fires, that was 3 weeks ago. Several days ago, this changed yet again. Mobi files/books (mobi extensions) have now been deprecated (blocked). This is an old format, Amazon had discontinued support for this in 2011, but it still worked on the built in Kindle reader. The mobi format no longer works on the built in Kindle reader. See the history of the Mobi file below.

The newer AZW3 file/eBook format is now working again for files from alternate sources. The mobi format will need to be converted if you get your eBooks from sources like the Internet Archive: https://archive.org/ . You would use the Calibre program to convert the mobi format to the AZW3 format. https://calibre-ebook.com/

History of the .MOBI file.

A French company developed the MOBI format in 2000, though its original extension was actually PRC.

After Amazon bought Mobipocket in 2005, they released the .MOBI format as a standard for their Kindle devices just a couple of years later. MOBI 7, the most recent version of MOBI, is also known as KF7 (standing for Kindle Fire version 7). Sometimes these files have an .AZW extension, due to the fact that they use Amazon’s own DRM system.

In 2011, however, Amazon discontinued support for the MOBI format and the .AZW3 became the preferred file extension for the Amazon Kindle devices and the Amazon’s marketplace.

In August 2022, Amazon officially retired the MOBI format and replaced it with EPUB, which is now the universal format for eBook, but does not open on the built in Kindle reader.

Today, MOBI files can still be opened using a compatible MOBI reader or by converting them to a more up to date format. Even though I recommend using Calibre you can also do this using Adobe products: https://www.adobe.com/uk/acrobat/resources/document-files/ebook-files/mobi.html .

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