code: public static void deliverMail (String[] recipients, String sender,
                                      String subject, String body,
                                      String[] headers, String[] values)
          throws IOException
      {
          if (recipients == null || recipients.length < 1) {
              throw new IOException("Must specify one or more recipients.");
          }
  
          try {
              MimeMessage message = createEmptyMessage();
              int hcount = (headers == null) ? 0 : headers.length;
              for (int ii = 0; ii < hcount; ii++) {
                  message.addHeader(headers[ii], values[ii]);
              }
              message.setText(body);
              deliverMail(recipients, sender, subject, message);
  
          } catch (Exception e) {
              String errmsg = "Failure sending mail [from=" + sender +
                  ", to=" + StringUtil.toString(recipients) +
                  ", subject=" + subject + "]";
              IOException ioe = new IOException(errmsg);
              ioe.initCause(e);
              throw ioe;
          }
      }
docs: Delivers the supplied mail, with the specified additional headers.