Steel Entry Door Paint Removal
How do you feel about harsh chemicals? I'd take it off the hinges and use the worst nastiest stripper I can find. And by stripper I mean paint stripper not the other kind!

I'd stay away from anything that claims it is safe. You don't want safe, you want done! You want the stuff with the skull and crossbones right there on the front, the bigger the better. 

So get your hose, big rubber gloves, and safety glasses and go to town.

Or you can use sandpaper and steel wool. You know, make a career out of it.