[GLLUG] British Gas DKIM failure?

[Carles Pina i Estany]

Hi,

On 28 Jan 2024 at 14:37:43, Marco van Beek via GLLUG wrote:
> On 27/01/2024 18:08, Henrik Morsing via GLLUG wrote:
> > 
> > I'm now getting the same from the Land Registry:
> > 
> > I wish there was a test I could do to check what is actually wrong...
> > 
> Okay, so this would indicate that it is more likely something wrong at your
> end rather than at theirs. I think that this point, I would start to wonder
> if there is anything at your end that is altering the email before it gets
> to the DKIM check.

this makes sense. I would also check if DKIM can be verified by, for
example, mails coming from gmail.com.

In my mail client: I view the headers to see the
"Authentication-Results". For an email from gmail.com to my mail server
with DKIM I see that it says "dkim=pass". But, note, that DMARC for
gmail.com says policy "none" and for the British Gas / Land registry I
think that says "policy=reject".

So, I wonder, does DKIM verification always fails for Henrik?
(e.g. wrong DNS lookups from DKIM, it happened to me). And, for some
domains, this is a reject and other domains, is "nothing happens".

[...]

> Maybe something in your system is altering something in a field that is
> being used by the British Gas and Land registry emails, like adding an
> "EXTERNAL" into the subject line before the DKIM test?

that's a good idea to check as well.

For reference, an email that I am checking the headers says:
Subject:From:To:Date:message-id:x-mailer-recipientid:fe
+edback-id:list-unsubscribe-post:list-unsubscribe:precedence:x-mailru-msgtype:x-campaignid:rep
+ly-to:MIME-Version:Content-Type

So, if the subject changed before verifying DKIM, it would not pass.

Cheers,

-- 
Carles Pina i Estany
https://carles.pina.cat
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