That Pesky “www” in Web Addresses
You may realize that if you enter a URL like rankmagic.com into your browser you get to the same page as when you enter www.rankmagic.com. It doesn’t seem to matter which way you do it. But for the search engines, it can make a difference.
The WWW refers to the World Wide Web, which many people consider to be synonymous with the Internet. Technically, it’s not. The WWW runs on the internet like email, but is not the Internet itself. The “www” part of an Internet address isn’t usually required, though, so you normally can use it or not when typing a URL into the address bar of your browser.
Search Engine Implications
Search engines see addresses with and without the “www” as separate addresses. Why should that matter? Because link authority is an essential factor in good ranking and use of the “www” can affect your link popularity. Here’s how:
Suppose you have 100 links pointing to  and another hundred links pointing to . Search engines will see that each URL has 100 inbound links, and that’s all you’ll get credit for. However, if they all pointed to  you’d get credit for all 200 links.
As I’ve written in the past, it can actually be worse than that, as it’s possible to have four different URLS for your home page like this:
This problem of multiple addresses for the same web page is called canonicalization. We have a full discussion of it on our web site.
What To Do?
You can’t control how other people link to your site and whether they use the “www” in the address or not. But you can set up a permanent redirect so that any time they don’t use the “www”, the link gets directed to the “www” version of your web address. We have instructions on how to fix your home page canonical issues on our web site.
Aside from redirecting external links to the “www” version of your address, you should also make sure your internal links pointing to your home page do the same. It’s very common for home page links from other pages on your site to include the actual page, as in www.example.com/l (there are several possible alternatives to index.html that your site may use). You should make sure that your own links to your home page don’t include that “index.html” part, and just point to www.example.com.