I've seen this before, when the header above the From header is broken:
Authentication-Results: server;
dkim=blah reason="blah";
From: "Valid" <addr...@example.tld>
To: mailop <mailop@mailop.org>
The parser thinks that the From: header is part of the previous header, thus
ignoring it and ending with a missing header error.
On Tue, 8 Nov 2022 13:41:57 -0800 John Stephenson via mailop
<mailop@mailop.org> wrote:
> We've seen the below failure for two different clients (each in one
> specific campaign) which resulted in lots of these failures at Gmail for
> those respective campaigns. Our Support/Ops team continue to insist that
> we sent these campaigns with the same exact from address/header/domain set
> up as all of the other campaigns launched on this day and that the issue
> must be on Gmail's side.
> I'm praying that somebody here has had experience with this failure and
> tracked down some subtle/quirky reason why an otherwise reliable sending
> MTA would encounter this failure?
>
> Best,
>
> John
>
>
> 550-5.7.1 [142.54.247.27] Our system has detected that this message is not
> RFC\r\n550-5.7.1 5322 compliant:\r\n550-5.7.1 'From' header is
> missing.\r\n550-5.7.1 To reduce the amount of spam sent to Gmail, this
> message has been\r\n550-5.7.1 blocked. Please visit\r\n550-5.7.1
> https://support.google.com/mail/?p=RfcMessageNonCompliant\r\n550 5.7.1 and
> review RFC 5322 specifications for more information.
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