Add "www" prefix to your website using IIS URL Rewrite

You can use following URL Rewrite rule to force all URLs in your website to start with "www":

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
    <rewrite>
        <rules>
              <rule name="Add WWW" stopProcessing="true">
              <match url="^(.*)$" />
              <conditions>
                 <add input="{HTTP_HOST}" pattern="^(?!www\.)(.*)$" />
              </conditions>
              <action type="Redirect" url="http://www.{C:0}{PATH_INFO}" redirectType="Permanent" />
           </rule>
        </rules>
    </rewrite>
</system.webServer>