It’s a red line for most publishers I’m afraid. I think there are legal reasons in addition to others for not being able to take on pre-published work. I would exhaust all potential submissions before going down the self-publish route although it didn’t hurt Mark Twain, George Orwell or Margaret Atwood to name a few. Also, I think the author of The Martian started it off as an on-line blog. So never say never.
