helper.addAttachment(MimeUtility.encodeText(fileName), file);

MimeUtility.encodeText(attachmentFilename)

if ((value.length() > 60) && (splitLongParameters)
            && (encodeParameters)) {
          int seg = 0;
          name = name + "*";
          while (value.length() > 60) {
            sb.addNV(name + seg, quote(value.substring(0, 60)));
            value = value.substring(60);
            ++seg;
          }
          if (value.length() > 0)
            sb.addNV(name + seg, quote(value));
        } else {
          sb.addNV(name, quote(value));
        }

private static final boolean splitLongParameters = PropUtil
      .getBooleanSystemProperty("mail.mime.splitlongparameters", true);

static {
     System.setProperty("mail.mime.splitlongparameters","false");
  }