function mailErr(){
  document.zayavka.onsubmit = function(){
        var eMail = document.getElementById('e-mailerror').value;
        var letter = /^[_\\.0-9a-z-]+@([0-9a-z][0-9a-z_-]+\.)+[a-z]{2,4}$/;
        var mails = document.getElementById('mails');
        if(!letter.exec(eMail) == false && letter.exec(eMail).length > 0){
          mails.style.display = 'none';
            return true;
        }
        else{
          mails.style.display = 'block';
            return false;
        }     
      }
}