The Webimax blog went through a redesign recently, and one of the sections that we were happy to add was an ask the experts section, where people can submit questions about online marketing, and get an answer from one of the many professionals at Webimax.
The following question about redirecting URLs wasn't one asked specifically about a questioner's site, but rather a practice that they've seen on the Web, and we thought the answer was worth sharing with a larger audience. If you have any questions about online marketing, please feel free to let us know.
I know of a company that is redirecting hundreds of vanity URLs (permanent redirects) to different pages within one single, large website. They are doing this for marketing purposes. They are not duplicating any content. Does this practice, directing several domains/urls to other pages within one site affect SEO? From what I've found, it doesn't do anything to help SEO but I want to ensure that it is not hurting.”
To answer a question like this, it's almost necessary to step into the mind of a search engineer since it's more about the reaction of search engines to a specific practice than it is about how someone optimizing a site might work to market that site.
The purpose of a permanent redirect is usually to tell visitors and search engines that a page has moved to a new address, and to deliver those visitors to that address. In most cases, the fact that it is a permanent redirect sends a signal to search engines that they should transfer PageRank and Hypertext relevance (the relevance that anchor text might pass along) to that new address from any links that are pointed to the old address, but they don't do that automatically.
Sometimes permanent redirects are used to anticipate some searches as well, such as Disney registering and redirecting mickeymouse.com to an internal Disney page on their website.
Google's servers are constantly reviewing the structure of a link graph of the Web, and looking for anomalies in it, such as where they might see a lot of low value pages (low PageRank) clustered together that all tend to point only to one other page, which then might point to another page in what appears to be an attempt to manipulate PageRank. They refer to that as a "dense subgraph" on their link graph, and it's one way for them to do things like uncover doorway pages and private blog networks.
That type of linking together of pages can send off a flag or alert to do more research of those pages, and the links between them to look for other webspam as well.
The type of activity that you describe, where lots of permanent redirects might be used to point to one site, in what might be an attempt to pass along anchor text from the links being used, could also potentially send a flag or alert to the search engines for an automated or manual review as well. It's possible that such activity could have some benefit to the site in question, at least initially.
But it's also likely that it is unusual enough to lead search engines to ignore any value those redirects might pass along or could lead to results such as a warning from Google (about unnatural links, in Google's Webmaster Tools) and/or result in a penalty.
We do know that when Google crawls the web, and collects URLs that it finds on pages, it does note things like whether or not those URLs go through redirects, and where those redirects lead to. There are at least a couple of patents from Google that describe such practices. Those patents also state that Google usually puts all of the 301 redirects to the side initially, and follows other links during a crawl. The permanent redirects are likely later analyzed in more detail before they might be placed into a queue for crawling.
There are also some costs associated with such a practice that may not be seen as quite as direct. The cost of including a lot of redirects on a site (temporary or permanent) is that they can make the pages of that site slower, since the handling of a redirect requires some extra processing work on the part of a server. That's why Google's PageSpeed tool recommends to site owners that they minimize the redirects found within their site.
Google's Matt Cutts also admitted in an interview about 2 years ago (in a followup email) that the use of internal redirects on a site can diminish the amount of PageRank distributed through that site because of the redirects - they just don't pass along as much PageRank. That can mean that the amount of PageRank distributed throughout the site as a whole can be less than it should be, and that all pages end up not ranking quite as high as they could.
So, having some domains redirect to another site, like mickeymouse.com redirecting to http://disney.go.com/mickey/#/home is probably fine. Having hundreds of permanent redirects pointing to the same site can potentially stand out, and may lead to closer scrutiny from the search engines.
For instance, if the sites being redirected never existed as stand alone sites (which could have been acquired), and appear to have been redirected primarily to manipulate anchor text and PageRank, those types of signals may result in penalties from the search engines.
Thanks for asking.