Nur externe Links ansprechen

Technik #1

$('a').filter(function() {
   return this.hostname && this.hostname !== location.hostname;
}).addClass("external");

Technik #2

$.expr[':'].external = function(obj) {
    return !obj.href.match(/^mailto\:/) && (obj.hostname != location.hostname);
};
$('a:external').addClass('external');

Technik #3

$('a:not([href^="http://your-website.com"]):not([href^="#"]):not([href^="/"])').addClass('external');

Technik #4

$('a').each(function() {
   var a = new RegExp('/' + window.location.host + '/');
   if (!a.test(this.href)) {
       // This is an external link
   }
});