DNSBounce message without boundaries

Email sent to no-such-user@domain.com should to create a DNS bounce MIME multipart message with DSN reason message as first BodyPart and DSN report-type with action and status as second BodyPart but DSNBounce message doesn't contain boundaries for each BodyPart which causes problems to process it.

Code used to dump DSNBounce message:

ByteArrayOutputStream outStream = new ByteArrayOutputStream();
msg.writeTo(outStream);
String content = outStream.toString();
LOGGER.info("Raw DSN message: \r\n" + content);