code: public void addTo(Address address) {
          assertArgumentNotNull("address", address);
          saveTo(address);
          try {
              message.addRecipient(RecipientType.TO, address);
          } catch (MessagingException e) {
              String msg = buildAddressSettingFailureMessage("to", address);
              throw new SMailMessageSettingFailureException(msg, e);
          }
      }
docs: ----------