//Verifica sintattica di un indirizzo mail
function checkMail(mail)
{
 correct = true;
 
 if(mail == "") {
     correct = false
 }
 else if(mail.indexOf("@")==-1 || 
        mail.indexOf("@")==0 || 
        mail.indexOf("@")==(mail.length-1) ||
        !(mail.indexOf("@")==mail.lastIndexOf("@")) ||
        mail.indexOf(".",mail.indexOf("@"))==-1 ||
        mail.indexOf(".",mail.indexOf("@"))==(mail.length-1) ||
        mail.lastIndexOf(".")==(mail.length-1) ||
        mail.indexOf(".",mail.indexOf("@"))==mail.indexOf("@")+1) {
        
        correct = false
 }
 else 
 {
       for (j=0;j<mail.length;j++) 
       {
          if (mail.charCodeAt(j)!=95 &&
              mail.charCodeAt(j)!=45 &&
              mail.charCodeAt(j)!=46 &&
              mail.charCodeAt(j)!=64 &&
             (mail.charCodeAt(j)<48 || mail.charCodeAt(j)>57) && 
             (mail.charCodeAt(j)<65 || mail.charCodeAt(j)>90) &&
             (mail.charCodeAt(j)<97 || mail.charCodeAt(j)>122)) 
          {    
             correct = false;
             break;
          }     
       }
 }    
 return correct;  
}