smonff/jsbin.UkIFuRi.css

## jsbin.UkIFuRi.css
input {
  height: 50px;
  width: 90%;
}

#message {
  color: red;
}

## jsbin.UkIFuRi.html
<!DOCTYPE html>
<html>
<head>
<script class="jsbin" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<meta charset=utf-8 />
<title>JS Bin</title>
<!--[if IE]>
  <script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<style>
  article, aside, figure, footer, header, hgroup,
  menu, nav, section { display: block; }
</style>
</head>
<body>
  <fieldset>
    <input type="textarea" placeholder="Ici essaie de mettre une adresse mail"/>
    <span id="message">Interdit !</span>
    <input id="validate" type="submit" value="Envoyer la purée" />
  </fieldset>
</body>
</html>

## jsbin.UkIFuRi.js
$("#message").hide();

$('input[type=textarea]').bind('input propertychange', function() {
   $("#message").hide();
   var checklength = $(this).val().length;

   if(checklength > 3){

     var text_area_content = $(this).val();
     console.log(text_area_content);
     var email_regex = /[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}/i;

     console.log($(this).val());

     if(text_area_content.match(email_regex)) {
       $('#validate').attr("disabled", "disabled");
       $("#message").show();
       console.log("!!!!! MAIL DÉTECTÉ !!!!!");
     } else {
       $('#validate').removeAttr("disabled");
     }
   }
});
	<!DOCTYPE html>
	<html>
	<head>
	<script class="jsbin" src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
	<meta charset=utf-8 />
	<title>JS Bin</title>
	<!--[if IE]>
	<script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
	<![endif]-->
	<style>
	article, aside, figure, footer, header, hgroup,
	menu, nav, section { display: block; }
	</style>
	</head>
	<body>
	<fieldset>
	<input type="textarea" placeholder="Ici essaie de mettre une adresse mail"/>
	<span id="message">Interdit !</span>
	<input id="validate" type="submit" value="Envoyer la purée" />
	</fieldset>
	</body>
	</html>
	$("#message").hide();

	$('input[type=textarea]').bind('input propertychange', function() {
	$("#message").hide();
	var checklength = $(this).val().length;

	if(checklength > 3){

	var text_area_content = $(this).val();
	console.log(text_area_content);
	var email_regex = /[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}/i;

	console.log($(this).val());

	if(text_area_content.match(email_regex)) {
	$('#validate').attr("disabled", "disabled");
	$("#message").show();
	console.log("!!!!! MAIL DÉTECTÉ !!!!!");
	} else {
	$('#validate').removeAttr("disabled");
	}
	}
	});