/*****************************************/
/*  phpBB3 Nofollow-Links mit Whitelist  */
/*  (c)2009 www.premium-hosting-24.de    */
/*  Fix by heimsath.org  :-)             */
/*****************************************/
	/* Variablen */
	$homeurl=$_SERVER['HTTP_HOST'];
	/* Konfiguration [START] */
	$whitelist = array(
	'www.your-domain.de',
        'www.your-domain.eu'
	);
	/* Konfiguration [ENDE] */
	$message = preg_replace('/(a class="postlink" href="(.*?)")/','a href="$2" class="postlink"',$message);
	$message = preg_replace('/(class="postlink")/','class="postlink" rel="nofollow" target="_blank"',$message);
	$message = preg_replace('/(href\=\"http\:\/\/'.$homeurl.'(.*?)\" class="postlink" rel="nofollow" target="_blank")/','href="http://'.$homeurl.'$2" class="postlink"',$message);
	# frei schalten der WhiteList 
	foreach($whitelist as $links) {
	$message = preg_replace('/(href="http\:\/\/'.$links.'(.*?)" class\=\"postlink\" rel\=\"nofollow\" target\=\"\_blank\")/','href="http://'.$links.'$2" class="postlink" target="_blank"',$message);
	}
	# target _blank valide machen:
	$trreplace='onclick="this.target='."'".'_blank'."'".'"';
	$message = preg_replace('/(target="_blank")/',$trreplace,$message);
/* phpBB3 Nofollow-Links mit Whitelist [END] */

Schönen Abend noch.