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However, unless you're going to republish content for the majority of your pages, it will only effect the page that it's on. If you're really worried about it, you can just tell the robots to ignore that page.
and you will probably see Supplemental Results on every article, which is a penalty.
I would only accept original articles that the author promises to not publish elsewhere and then search for text of that article before you publish it to make sure someone else hasn't posted it first because if they have you will likely be the one to get the SR penalty.