Maintaining a single canonical domain is an important part of managing a website. If both the www and non-www versions of a site are accessible, browsers and search engines treat them as separate hostnames, which can lead to duplicate content, inconsistent cookies, authentication problems, and unexpected security behavior.

IIS URL Rewrite provides a simple solution by permanently redirecting all requests to the www hostname to the preferred non-www version of the website. The redirect preserves the original path and query string, ensuring that visitors and search engines arrive at the correct page without broken links or lost parameters.

Using a permanent ([ HTTP 301 ]) redirect also helps consolidate search engine rankings, improves URL consistency throughout your application, and simplifies future development by ensuring that every request uses the same hostname. Whether you're building an ASP.NET WebForms application, an ASP.NET MVC site, or a Classic ASP website, implementing a canonical domain redirect is considered a best practice and typically requires only a single URL Rewrite rule within the site's [ web.config in IIS ] file.

<rewrite>
  <rules>	
    <rule name="Redirect www to non-www" stopProcessing="true">
       <match url="(.*)" />
          <conditions>
            <add input="{HTTP_HOST}" pattern="^www\.YourDomain\.com$" />
          </conditions>
          <action type="Redirect" url="https://YourDomain.com/{R:1}" redirectType="Permanent" appendQueryString="true" />
   </rule>
 </rules>
</rewrite>