I’ve been trying to figure out this question for quite sometime; how, if at all, does having multiple domains pointed towards the same site affect page rank? I think I’ve found the answer. After briefly speaking with Richard John Jenkins, a Search Engine Optimization and Marketing Web Search Engineer, the head IT guy at my work, and searching through various Web design and Google forums, I’ve come to a conclusion. Yes, it does affect your page rank, but not in a positive way.
Say you have a Web server, with domain.com on it, and you also want to point domain.org to the same site. If you just have both domains pointed to the same site, then you’d be able to browse the site under either of the domain names you’ve pointed to it. To Google, as far as I can tell, this is considered Black Hat SEO, because you are giving yourself an unfair advantage in Web real estate. Both domains can be indexed, both containing the same content. This is bad.
Instead, what you should do is have one of the domains point to a 301 redirect page. This way, people can still use that second domain name to get to your site, and any external links your second domain receives will be passed on to your main domain name.
This question arose when I found out that Montage, Inc. (the company for which I currently work), had two domain names pointed to the same site (montagefs.com and montagefurnitureservices.com) and our page rank was going nowhere, even though I had optimized the site to the best of my ability and it had been a few months since the new design was uploaded.