How can I force my site to add "www." to the URL?

Scenario:

Customer types in YOURSITE.com when trying to enter your website.

In most cases this will let them get to your site fine.

BUT, if you’ve configured your site to use www.YOURSITE.com in all the URLs it generates, then the customer’s next click will attempt to change the URL and (on some servers) may log them out if they were attempting login, etc.

There are a couple things to keep in mind to handle this:

• Always be consistent in your use of your domain name. If you’re going to use www.YOURSITE.com, be sure to use it exactly that way everywhere. Don’t drop the www. unless you do it consistently in all places.
• In your SSL certificate, when you register one, you must specify a domain name. Again, be consistent. If you’re using www in your URL, use it in your SSL certificate too.
• Ensure that your hosting company has configured a www address as an alias to your domain name so that “both” will work – otherwise visitors might get a “domain not found” error instead of your site.
• If you are running on an Apache webserver, you can set up a .htaccess rule to automatically add the www into the URL if the customer forgets to include it. The following is what you’d put in your .htaccess to accomplish this:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^YOURSITE.com$
RewriteRule ^(.*)$ http://www.YOURSITE.com/$1 [R=301,L]