Do you really need EPUB? If you want to read an Amazon book on a Kobo, yes. But if you want to read a non-Amazon book on a Kindle, Amazon allows you to email EPUB files to your Kindle, where they are auto-converted to KFX on Amazon’s cloud.
: Amazon moved from the older AZW3 (Kindle Format 8) to the more advanced KFX (Kindle Format 10) to power "Enhanced Typesetting"—features like smarter hyphenation and responsive layouts. convert kfx-zip to epub