Additional information: Capture.PNG is a screen shot of the email that software-lab.de sent me, which contained my own message.
So I wondered if my own email that I sent to software-lab.de contained the extra data! To check this, I recreated my original message, step by step.. but changed the TO: address to another address instead of firstname.lastname@example.org... By that method, here is what I originally sent to the list: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 MIME-Version: 1.0 PiBJZiBwZW9wbGUgYXJlIGN1cnJlbnRseSB3b3JraW5nIG9uIGltcHJvdmluZyB0aGUgbWFpbGlu ZyBsaXN0Lg0KDQpJIHdvdWxkIGxpa2UgdG8gc3RvcCByZWNlaXZpbmcgYmluYXJ5IGp1bmsgYXQg dGhlIGVuZCBvZiBwbGFpbi10ZXh0IGVtYWlscy4NCg0K I hope that helps! Cheers, --Dave -----Original Message----- From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Loyall, David Sent: Thursday, April 20, 2017 1:11 PM To: email@example.com Subject: RE: Header parsing See attached PNG. [snip]