Custom 404 on Microsoft IIS

Server Config
3

I was starting to think that no one is using IIS out there.

I think it is 8.5, I only found out because of this Site ignoring htaccess redirects - need IIS web.config
I’m more used to dealing with htaccess, web.config is new to me. I only have FTP access at present, so the web.config file is my only means to set thing up. It looks something like this.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
      <httpRedirect enabled="true" exactDestination="true" httpResponseStatus="Permanent">
         <add wildcard="*.html" destination="/" />
      </httpRedirect>
      <httpErrors>    
       <remove statusCode="404" subStatusCode="-1" />                
       <error statusCode="404" path="http://www.example.com/404.shtml" responseMode="Redirect" />
      </httpErrors>
   </system.webServer>
    <system.web>
        <customErrors mode="RemoteOnly" defaultRedirect="http://www.example.com/error.shtml" />
    </system.web>
</configuration>

The redirects appear to work, but WMT says they are soft 404s.