For some time now I’ve been telling clients and friends that publishing duplicate content will not cause you to receive a penalty but that Google will only choose one version of a unique piece of content that it believes to be the authority and refuse to allow other copies to be indexed. So if you publish a copy of one of my blog posts, Google will likely allow my original copy to rank but yours won’t be found.
I think I’ve discovered that enough duplicate content can actually do harm to a domain.
I had an old site we’ll call oldsite1.com. I was publishing fresh, unique, well written content there several times a day. oldsite1.com would always enjoy nice rankings for the content published there and new content was indexed quickly. I had always intended to eventually 301 redirect all of oldsite1.com’s pages to newsite1.com which would be hosting identical content. Past experience tells me that the 301 will cause all of oldsite1.com’s backlinks and authority to transfer over to newsite1.com and within days I’d see the new site perform nearly as well as the old site’s.
Now here is the mistake I made: some time ago I setup newsite1.com to mirror oldsite1.com (for some offline promotional reasons). I had zero backlinks to newsite1.com but it was crawled and indexed anyway. Obviously it was 100% duplicate content and nothing but duplicate content. But I didn’t worry too much about it. The day came to 301 redirect and within days the traffic plummeted. Its been several weeks and no recovery has happened.