This library produced MimeMessage instances where the MessageId cannot be fixed. This is because when sending MimeMessage with Jakarta Mail, the ID is always overwritten by a generated one. to fix this, this class should return a subtype that overrides the ID, if given by the user, as follows:

    @Override
    protected void updateMessageID() throws MessagingException {
        if (messageId == null || messageId.length() == 0) {
            super.updateMessageID();
        } else {
            setHeader("Message-ID", messageId);
        }
    }