function controlla(s){
var a = false; 
var res = false; 
if(typeof(RegExp) == 'function') 
{ 
var b = new RegExp('abc'); 
if(b.test('abc') == true){a = true;} 
} 
 
if(a == true) 
{ 
reg = new RegExp('^([a-zA-Z0-9\\-\\.\\_]+)'+ 
'(\\@)([a-zA-Z0-9\\-\\.]{2,255})'+ 
'(\\.)([a-zA-Z]{2,4})$'); 
res = (reg.test(s)); 
} 
else 
{ 
res = (s.search('@') >= 1 && 
s.lastIndexOf('.') > s.search('@') && 
s.lastIndexOf('.') >= s.length-5);
} 

if(res==false||s=='email@domain.com'){alert("Inserisci un indirizzo e-mail valido.");
	return false;}

else{return true;}
	
}