Keep in mind that Received: lines that look falsified in any way
are universally treated as a sure sign of spam.
My friends comment often that my mail is marked as spam, so, upon
reading this, I thought, does the absence of the earliest received
header cause the mail to be marked as spam? Upon further though,
I concluded that, maybe it contributes, because commercial spam
processing seems so arbitrary these days, but it's not the main cause.
I am 100% certain that some spam filters look at Received headers.
Now, I think they SHOULD regard them with a grain of salt, but that's
the world we live in today.
I was curious about your messages getting marked as spam, so I looked at
your message. I noticed this in the header:
Arc-authentication-results: i=1; pb-mx20.pobox.com;
arc=none (no signatures found);
bimi=skipped (DMARC did not pass);
dkim=fail (message has been altered, 2048-bit rsa key sha256)
header.d=fastmail.nl header.i=@fastmail.nl header.b=lG3IOekl
header.a=rsa-sha256 header.s=fm2 x-bits=2048;
dkim=fail (message has been altered, 2048-bit rsa key sha256)
header.d=messagingengine.com header.i=@messagingengine.com
header.b=mjvrWA29 header.a=rsa-sha256 header.s=fm2 x-bits=2048;
dmarc=fail policy.published-domain-policy=none
policy.published-subdomain-policy=none policy.applied-disposition=none
policy.evaluated-disposition=none policy.override-reason=mailing_list
policy.arc-aware-result=fail
(pobox.com is my email provider, and I guess now they're part of
fastmail?)
So at least somebody at my side thinks one of your DKIM signatures is
invalid. And you have TWO DKIM signatures; one from fastmail.nl, but
another from messagingengine.com. I lack the energy to track down
why your DKIM signature is invalid, but that might be worth doing.
--Ken