code: public String notifications_sendEmailPlain(Collection<Integer> recipientIds, CharSequence subject, CharSequence text)
      throws FacebookException, IOException {
      return notifications_sendEmail(recipientIds, subject, /*fbml*/null, text);
    }
docs: Sends a notification email to the specified users, who must have added your application.
  You can send five (5) emails to a user per day. Requires a session key for desktop applications, which may only
  send email to the person whose session it is. This method does not require a session for Web applications.
  
  @param recipientIds up to 100 user ids to which the message is to be sent
  @param subject the subject of the notification email (optional)
  @param text the plain text to send to the specified users via email
  @return a comma-separated list of the IDs of the users to whom the email was successfully sent
  @see <a href="http://wiki.developers.facebook.com/index.php/Notifications.sendEmail">
  Developers Wiki: notifications.sendEmail</a>