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If you are sure it has a penalty, I would 404 the page and get the links removed if possible

In guest posting you can use only fresh content if that content was not published anywhere else then you can resubmit it in other blog. If the content is yours, all you would have done is grant the owner of the other website permission to post your work. If the content is nowhere to be found, it could now hardly be considered to be a duplicate of something else.

Hi Gareth, The best practice for this is unfortunately TEDIOUS. You'd need to 301 each page to the correlating page on the new domain, as well as do a 301 redirect from the root domain to the new root domain. Redirecting the entire domain won't make the internal 301's obsolete, but will only pass the page authority of the index of the root domain to the new domain. So essentially you'll lose individual page authority from any pages that haven't been 301 redirected individually. Hope that makes sense and helps. It's tedious, but there are likely some tools out there to mitigate the time involved. Thanks, Anthony

It's ahrd to address in blog comments, but these things can be very situational. In a perfect world, I don't like those phantom folder levels for 2 reasons: (1) Someone will eventually try to link to or access one, including possibly Google, and that may lead to odd behavior. I've seen claims Google will extrapolate URLs, but have never seen clear proof. (2) It just makes for long URLs that, in this case, look a bit spammy. Practically, is it making a difference? They aren't being indexed, so that's certainly a positive sign - it indicates no weird extrapolation by Google and no inbound links to those levels. At the same time, as discussed in my post, revamping your entire URL structure does carry risk. So, it's not ideal (IMO), but I'm not sure I'd mess with it unless you're changing URLs for other reasons (then, do it all at once).