My bad. This header is only added before sending the message to the next hop. In other words, it is only added when you run Xeams in Hybrid or Firewall mode. It is not added in Stand-alone mode. I assume you're using Xeams in stand-alone. Is that correct?

Could you please tell me a use-case why you need this header if all you're doing is to pull the messages using an IMAP/POP3 client? I can certainly submit a feature request for this.