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After years using a .net.au site, my client has purchased the .com.au version of the same domain. I've now set up a new, responsive website using a wordpress template with new content, but used a similar page structure. I've asked their web developer to now do a 301 permanent redirect on each old page from .net.au site to it's new .com.au page, but he has refused, saying it would be bad for long term SEO. Instead, he says they should run both sites (which I thought would cause duplicate content issues). Both domains are hosted with the same company. I thought as long as the 301 redirects were done on a page by page basis, there were no issues? I'm no SEO expert, (which he claims to be), so I just wanted to get another opinion on what best practice would be in this instance.