Even though there are "pre-primed" doors on the market, you still need to prime them. And it's something you can do yourself.
The first thing is, if it's not recoated within 30 days, it has to be re-primed. Primers are very porous when they are new. It allows the top coat to soak in to those pores, and when the pores close, the top coat will bind together. If you don't within 30 days, those pores close and the top coat can't stick. That's what we believe happens with these metal doors. And when you paint them it's a hard surface. It's not that paint will just fall off, it just won't bond.
The other thing is many stores will tell you is that a latex primer or top coat is just fine without an oil primer. But what happens to a door without the proper primer? Even with a good latex top coat, you can see all around the door where people's hands have touched. The paint is gone and it's very dirty. Latex paint is porous, so all that dirt from grabbing the door will soak into that top coat of paint. We do believe there are good latex top coats, but we also believe you need an metal based primer underneath.
It's very important that you don't buy normal oil house primer. It's full of linseed oil and that's good for a house. But, on a door you have a soft surface that would get messed up and stick to the weather stripping. So buy a metal primer. For the top coat it has to be a quality latex paint. Cheaper paint means less durability. If you go too cheap, blocking happens. That's where paint sticks to a weather strip. Now how to get back to the base coat, you can sand it off, but it clogs up the sandpaper. Lacquer thinner and sponge it on, you will be able to get the paint off correctly. Oil based metal primer, premium top coat -- that's the solution.