Note that only a few MOBI retailers allow you to enter a Kindle PID, and in particular those which use MobiPocket as their wholesaler don't any more. See
A Beginner's Guide to Kindle Content (item 4 in the 1st post with other retailers listed in later posts). You still have to run kindlefix.py but this does not remove the DRM, it just allows you to read your ebook, already authorized for your Kindle, on your Kindle.