[No source IP address found, cannot proceed.]

As it turns out this was caused by my sending mailserver (Mailu) which replaces Recevied lines (even in attachments).

One solution would be to force Thunderbird to send the attachment as base64-encoded. But I have not found an option for this.

I created a ticket in Mailu's tracker https://github.com/Mailu/Mailu/issues/1660 but the behavior seems to stem from Postfix's handling of filters, which for some reason get applied inside the message.

[No source IP address found, cannot proceed.]

Hi @petzl I hoped the details can be kept non-public but let's look at the real details:

https://www.spamcop.net/sc?id=z6675008964zc1dc39ff8aa771b6633043fa7cd917c5z

The owners of these IP ranges generally are not very cooperative until they see their IPs show up on bloacklists.

[No source IP address found, cannot proceed.]

I get lines like the following ones (and 4 more)

Received:  from authenticated-user (PRIMARY_HOSTNAME [PUBLIC_IP])
Ignored

Received:  from authenticated-user (PRIMARY_HOSTNAME [PUBLIC_IP]) by fmx10.freemail.private with SMTP; 9 Oct 2020 12:40:37 +0200
Ignored

Received:  from authenticated-user (PRIMARY_HOSTNAME [PUBLIC_IP]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx.onbox.hu (Postfix) with ESMTPS id 4C74NP0ZfFzbtP for <x>; Fri, 9 Oct 2020 12:40:36 +0200 (CEST)
Ignored

When I forward the email the source contains proper-looking Received lines like this:

Received: from srv2.subonline.live (ip19.ip-51-zzz-169.eu [51.zzz.169.19])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by mx.onbox.hu (Postfix) with ESMTPS id 4C74NP0ZfFzbtP
	for <zzz@freemail.hu>; Fri,  9 Oct 2020 12:40:36 +0200 (CEST)

(note: "zzz" my edit)

Is there a ticketing system where I can submit the raw input/output privately?

Thanks in advance!