Quote from JeffersonW on April 24, 2018, 9:15 pm

Epub is a standard format of almost all ebooks these days. It is really a self contained series of HTML (web pages) complete with CSS (Cascading Style Sheets) that tell the browser (e-reader) how to display the information. Cool right?

Mobi is incredibly close to Epub - it's just Amazon's specific flavor.

As mentioned in previous posts - you'll receive both formats.