Are you aware that there is a difference between using http://www.domainexample.com and http://domainexample.com for your site links?  If you use Google Webmaster Tools (GWT) you may have noticed in the settings area (as shown below) there is an option to set your Preferred Domain in Google Webmaster Tools.

Before I get into how you adjust your preferred domain setting in Google Webmaster tools I want to address why there is a difference between www and non www websites.  You can of course not make this change but we strongly recommend that you do!
Why? For Search Engines Optimization (SEO) reasons you should always use the same address for your website links so choose either with www or without www and stick to it. This is called canonicalization and it means picking the best website address or URL when you have a choice.

Because www.domainexample.com is not the same as domainexample.com and if you have different inbound links to both URLs, this could cause two problems:

1. Some search engines will think that this is a duplicate content and penalize your site for this.  The search engines historically do not like duplicate content.  Being penalized is rare these days; however, Google will only show results for 1 of the domains which leads to the next reason.
2. Sharing your website links (www and non www) will affect your Google PageRank.  To increase your Google PageRank you need to have high quality and relevant links going back to your website. If you have 2,500 inbound links to www.domainexample.com and 225 inbound links to domainexample.com then you will have different PageRank for both versions of the same website and you will lose valuable inbound links because they will be split into links for both websites.

To address this problem again pick one of the versions (we like the www version) and from now on only reference that address within your website and external websites.  You can also set a 301 permanent redirect on your server from non www to www.

Next and to get to the point of this blog post you need to set the correct domain in Google’s Webmaster Tools, click “Preferred domain” and choose the same URL that you chose in the previous step.  You are probably coming across this blog post because you went to go set your preferred domain in Google Webmaster Tools and got an error that you need to verify the other domain.  I know this is probably the case because that is what happened to us and after a lot of trial and error we finally figured out how easy it was to solve this problem.

Here are the easy steps on how you set your preferred domain:

1. Log onto Google Webmaster Tools
2. Click on settings on left side and choose the preferred domain
3. You will then get the verify the other domain notice
4. Click on Back to Home on Top Right corner
5. Click on the Add A Site link on top of the Google Webmaster Tools home page
6. Add the other version of your domain such as domainexample.com if the other version is www.domainexample.com
7. After verifying this new domain click on settings and then set the preferred domain as the same as the other site.  As a reminder just in case you have not verified a website in a while in Google Webmaster Tools you verify your GWT account for www.domainexample.com either by using an HTML meta tag or using HTML file upload method.  If you are asked to verify your site, select the verification method that you used earlier for verifying your www-version of site, www.domainexample.com and hit “Verify” .Your website would be automatically verified and would be added to your sites in GWT.
8. That’s it!  You will then see a note that “The Preferred Domain For Your Site Has Changed” and if you look in the settings area of both sites you will see they are now set to your preferred domain.

Now you have successfully set your preferred domain as “www.domainexample.com” i.e to the www-version of your website.  Let us know if you have any questions or if you found this to be helpful.