var maxMessageHeight = 70;
document.observe("dom:loaded", function(){
    $$('.messageBody p').each(function(element){
        if(element.getHeight() > maxMessageHeight){
            openLink = new Element('a', {'href': '#', 'onclick': 'return false;'});
            openLink.observe('click', function(){toggleMessage(element);});
            element.ancestors()[0].appendChild(openLink);
            toggleMessage(element);
        }
    });
});

function toggleMessage(element){
    if(element.getHeight() > maxMessageHeight){
        element.style.height = maxMessageHeight+'px';
        element.style.overflow = 'hidden';
        element.nextSiblings()[0].className = 'toggleMessageLinkOpen';
        element.nextSiblings()[0].update('aufklappen');
    } else {
        element.style.height = 'auto';
        element.nextSiblings()[0].className = 'toggleMessageLinkClose';
        element.nextSiblings()[0].update('zuklappen');
    }
    return false;
}