Since you are producing a book to publish, rather than just for your own use, I suggest using Amazon's tools for the conversion.
Amazon's
Kindle Previewer 3 can convert from either EPUB or DOCX to Master MOBI, which includes both the old-style MOBI and AZW3 in one file. This is the format most acceptable to Amazon. (Use the File>Export function to save the Master MOBI.) It also lets you know whether or not your book will support Enhanced Typesetting for the best reading experience on newer Kindle devices.
(For the future you are better off asking this sort of question in the
Kindle Formats forum. That forum is used for technical discussion by those who publish Kindle books.)