Código HTML, PHP, JS

<form id="form" action:"MailHandler.php">
       <div class="success_wrapper">
       <div class="success">Su consulta ha sido enviada!<br>
       <strong>Entraremos en contacto a la mayor brevedad posible.</strong> </div></div>
       <fieldset>
       <label class="name">

       <input type="text" value="Nombre:" name="name">
       <br class="clear">
       <span class="error error-empty">*Nombre inválido.</span><span class="empty error-empty">*Campo necesario.</span> </label>
       <label class="email">
       <input type="text" value="email:" name="email"> 
       <br class="clear">
       <span class="error error-empty">*email inválido.</span><span class="empty error-empty">*Campo necesario.</span> </label>
       <label class="message">
       <textarea name="message">Mensaje:</textarea>
       <br class="clear">
       <span class="error">*El mensaje es muy corto.</span> <span class="empty">*Campo necesario.</span> </label>
       <div class="clear"></div>
       <div class="btns"><a data-type="submit" class="link1">Enviar.</a>
       <div class="clear"></div>
       </div></fieldset></form> 

<?php
 $owner_email = "EMAIL@DOMINIO.X";
 $headers = 'From:' . $_POST ["email"];
 $subject = 'Nuevo mensaje desde el formulario ' . $_POST["name"];
 $messageBody = "";
 
 if($_POST['name']!='nope'){
  $messageBody .= '<p>Cliente: ' . $_POST["name"] . '</p>' . "\n";
  $messageBody .= '<br>' . "\n";
 }
 if($_POST['email']!='nope'){
  $messageBody .= '<p>email: ' . $_POST['email'] . '</p>' . "\n";
  $messageBody .= '<br>' . "\n";
 }else{
  $headers = '';
 }
if($_POST['message']!='nope'){
  $messageBody .= '<p>Mensaje: ' . $_POST['message'] . '</p>' . "\n";
 }
 
 if($_POST["stripHTML"] == 'true'){
  $messageBody = strip_tags($messageBody);
 }
 
 try{
  if(!mail($owner_email, $subject, $messageBody, $headers)){
   throw new Exception('mail failed');
  }else{
   echo 'mail sent';
  }
 }catch(Exception $e){
  echo $e->getMessage() ."\n";
 }
?>

//forms
;(function($){
 $.fn.forms=function(o){
  return this.each(function(){
   var th=$(this)
    ,_=th.data('forms')||{
     errorCl:'error',
     emptyCl:'empty',
     invalidCl:'invalid',
     notRequiredCl:'notRequired',
     successCl:'success',
     successShow:'4000',
     mailHandlerURL:'MailHandler.php',
     ownerEmail:'EMAIL@DOMINIO.X',
     stripHTML:true,
     smtpMailServer:'XXXXXXXX',
     targets:'input,textarea',
     controls:'a[data-type=reset],a[data-type=submit]',
     validate:true,
     rx:{
      ".name":{rx:/^[a-zA-Z'][a-zA-Z-' ]+[a-zA-Z']?$/,target:'input'},
      
      ".email":{rx:/^(("[\w-\s]+")|([\w-]+(?:\.[\w-]+)*)|("[\w-\s]+")([\w-]+(?:\.[\w-]+)*))(@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$)|(@\[?((25[0-5]\.|2[0-4][0-9]\.|1[0-9]{2}\.|[0-9]{1,2}\.))((25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\.){2}(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[0-9]{1,2})\]?$)/i,target:'input'},
      
      ".message":{rx:/.{20}/,target:'textarea'}
     },
     preFu:function(){
      _.labels.each(function(){
       var label=$(this),
        inp=$(_.targets,this),
        defVal=inp.val(),
        trueVal=(function(){
           var tmp=inp.is('input')?(tmp=label.html().match(/value=['"](.+?)['"].+/),!!tmp&&!!tmp[1]&&tmp[1]):inp.html()
           return defVal==''?defVal:tmp
          })()
       trueVal!=defVal
        &&inp.val(defVal=trueVal||defVal)
       label.data({defVal:defVal})        
       inp
        .bind('focus',function(){
         inp.val()==defVal
          &&(inp.val(''),_.hideEmptyFu(label),label.removeClass(_.invalidCl))
        })
        .bind('blur',function(){
         _.validateFu(label)
         if(_.isEmpty(label))
          inp.val(defVal)
          ,_.hideErrorFu(label.removeClass(_.invalidCl))           
        })
        .bind('keyup',function(){
         label.hasClass(_.invalidCl)
          &&_.validateFu(label)
        })
       label.find('.'+_.errorCl+',.'+_.emptyCl).css({display:'block'}).hide()
      })
      _.success=$('.'+_.successCl,_.form).hide()
     },
     isRequired:function(el){       
      return !el.hasClass(_.notRequiredCl)
     },
     isValid:function(el){       
      var ret=true
      $.each(_.rx,function(k,d){
       if(el.is(k))
        ret=d.rx.test(el.find(d.target).val())          
      })
      return ret       
     },
     isEmpty:function(el){
      var tmp
      return (tmp=el.find(_.targets).val())==''||tmp==el.data('defVal')
     },
     validateFu:function(el){       
      el.each(function(){
       var th=$(this)
        ,req=_.isRequired(th)
        ,empty=_.isEmpty(th)
        ,valid=_.isValid(th)        
       
       if(empty&&req)
        _.showEmptyFu(th.addClass(_.invalidCl))
       else
        _.hideEmptyFu(th.removeClass(_.invalidCl))
       
       if(!empty)
        if(valid)
         _.hideErrorFu(th.removeClass(_.invalidCl))
        else
         _.showErrorFu(th.addClass(_.invalidCl))        
      })
     },
     getValFromLabel:function(label){
      var val=$('input,textarea',label).val()
       ,defVal=label.data('defVal')        
      return label.length?val==defVal?'nope':val:'nope'
     }
     ,submitFu:function(){
      _.validateFu(_.labels)       
      if(!_.form.has('.'+_.invalidCl).length)
       $.ajax({
        type: "POST",
        url:_.mailHandlerURL,
        data:{
         name:_.getValFromLabel($('.name',_.form)),
         email:_.getValFromLabel($('.email',_.form)),
         
         message:_.getValFromLabel($('.message',_.form)),
         owner_email:_.ownerEmail,
         stripHTML:_.stripHTML
        },
        success: function(){
         _.showFu()
        }
       })   
     },
     showFu:function(){
      _.success.slideDown(function(){
       setTimeout(function(){
        _.success.slideUp()
        _.form.trigger('reset')
       },_.successShow)
      })
     },
     controlsFu:function(){
      $(_.controls,_.form).each(function(){
       var th=$(this)
       th
        .bind('click',function(){
         _.form.trigger(th.data('type'))
         return false
        })
      })
     },
     showErrorFu:function(label){
      label.find('.'+_.errorCl).slideDown()
     },
     hideErrorFu:function(label){
      label.find('.'+_.errorCl).slideUp()
     },
     showEmptyFu:function(label){
      label.find('.'+_.emptyCl).slideDown()
      _.hideErrorFu(label)
     },
     hideEmptyFu:function(label){
      label.find('.'+_.emptyCl).slideUp()
     },
     init:function(){
      _.form=_.me      
      _.labels=$('label',_.form)

      _.preFu()
      
      _.controlsFu()
              
      _.form
       .bind('submit',function(){
        if(_.validate)
         _.submitFu()
        else
         _.form[0].submit()
        return false
       })
       .bind('reset',function(){
        _.labels.removeClass(_.invalidCl)         
        _.labels.each(function(){
         var th=$(this)
         _.hideErrorFu(th)
         _.hideEmptyFu(th)
        })
       })
      _.form.trigger('reset')
     }
    }
   _.me||_.init(_.me=th.data({forms:_}))
   typeof o=='object'
    &&$.extend(_,o)
  })
 }
})(jQuery)
$(window).load(function(){
 $('#form').forms({
  ownerEmail:'EMAIL@DOMINIO.X'
 })
})