[GLLUG] British Gas DKIM failure?

Henrik Morsing henrik at morsing.cc
Fri Jan 12 15:48:17 UTC 2024

Good afternoon,

Not dircetly Linux, sorry, but British Gas has spent the last year sending me letters saying they can't email me. When I look into it, their emails are rejected based on a bad DKIM signature.

The problem is, not receiving the email, how can I find out what the problem is? mxtoolbox says their setup is fine, but that surely can't check the signature inside one of their emails.

What is slightly odd is that DMARC policy is set to none, so shouldn't reject anything anyway.

I can't say I'm a DKIM/DMARC expert, but this is what I see:

Dec 22 12:37:12 emil opendkim[768]: 2F7612233E: s=mailjet d=britishgas.co.uk a=rsa-sha256 SSL error:04091068:rsa routines:int_rsa_verify:bad signature
Dec 22 12:37:13 emil opendmarc[3858740]: 2F7612233E: britishgas.co.uk fail
Dec 22 12:37:13 emil postfix/cleanup[3996586]: 2F7612233E: milter-reject: END-OF-MESSAGE from o94.p12.mailjet.com[]: 5.7.1 rejected by DMARC policy for britishgas.co.uk; from=<296f63a1.CAAABPhWdncAAAAAAAAAAKg7aSYAAYCqUv4AAAAAABBDggBlhYBF at a1065858.bnc3.mailjet.com> to=<morsing at morsing.cc> proto=ESMTP helo=<o94.p12.mailjet.com>

Not sure where to go from here though. Smells like their problem to me, but I don't want to tell them that without proof. Any hints?

Henrik Morsing

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