Script

jQuery(function($){
    $('#email').bind('keyup blur',function(){
        var txt = $(this).val();
        var txtLength = txt.length;
        
        if(txt && txtLength>0){
            if(txt.match(/^[^@ 　\t\n\r]+@[\w\-]+\.[\w\-\.]+$/)){
                $(this).next().remove().end().after('<span class="ok">valid</span>');
            }else{
                $(this).next().remove().end().after('<span class="err">invalid</span>');
            }
        }else{
            $(this).next().remove();
        }
    });
});

Demo