In his latest video Matt Cutts head of Google’s anti-spam team has answered a question relating to whether it is bad practice to link multiple domains together. In the question Matt is asked if a client has 20 domains is it OK to link them all together?
Matt questions first of all why would you need twenty domains and points out that if they are all connected to spammy terms such as “cheap-online-casinos” then it would be best not to link them as it would appear to be a link network. He then went on to say that if the reason for so many domains is to provide different versions of your website in different countries then it would be OK to link them. However, he did also add that it might be better not to include links to each site in the footer but to either have a separate page that listed all the different domains or to use flags as the links to them.
As with most, if not all, things Google search related the real answer is does the practice in question add value to a user’s experience of the website, If you have got twenty domains that are all offering the same product or service but have different domains with their own look and feel then it would not matter which site you went to, you would still see basically the same material and so having a link from one site to another would not give the user anything new in terms of content. In the example of domains offering different language versions of the same site then there is an intrinsic value in letting users who arrive at a .com domain but who are German that there is a German language version of the site available on the .de domain. This provides a better overall user experience and so would not be penalised by Google if implemented correctly.
This technique should not be confused with a 301 redirect. This is where you have content that has been moved from one domain to another. There are likely to be links that point to the pages on the original domain from other sites. When that content moves by using a 301 redirect you are telling visitors to that page that the content has moved and send their browser to the new location. Again this helps to provide a better user experience as it reduces the number of dead links that are on the web.
If you are using multiple domains for basically the same purpose you might find that you would be better served just using one domain and offering higher quality content to attract users and links and improve your search engine rankings by optimising in a more white hat way.