The LMTP runner should accept messages to the -bounces address without a Message-ID: header.
Currently the LMTP runner rejects any message without a Message-ID: header. This header is important for archiving so not accepting list posts without it makes sense. However, RFC 5322 and predecessors say only "every message SHOULD have a "Message-ID:" field", i.e., it is not required, and DSNs have been observed in the wild without it.
Since the Message-ID: header is not an important part of bounce processing, the LMTP runner should accept messages to the list-bounces address without it.