$HTTP["host"] == “www.<example>.com” {
   server.document-root = “/www/sites/<example>.com/www/”
}

Trap all traffic not directed to the main site (regex non-match), then filter remaining traffic headed to the correct domain with the wrong host (regex) and redirect to the main site.

$HTTP["host"] !~ “^(www|mail)\.(<example>\.com)$” {
   $HTTP["host"] =~ “(^|.*\.)<example>\.com” {
      url.redirect = ( “^/(.*)” => “http://www.<example>.com/” )
   }
}

This is an effective defensive technique to guard against redundant content bombing in which a competitor submits URLs containing different hosts with the same domain to search engines making it appear as if the target site has several pages of identical content