[GLLUG] British Gas DKIM failure?

[Carles Pina i Estany]

Hi,

On 17 Jan 2024 at 12:30:15, Henrik Morsing via GLLUG wrote:
> On Mon, Jan 15, 2024 at 07:45:25PM +0000, Carles Pina i Estany via GLLUG wrote:
> > 
> > Hi,
> > 
> 
> Hi,
> 
> > 
> > Side note, almost unrelated.
> > 
> > In a personal/family server I have a nightly script that sends me which
> > emails have been rejected by the server. Why? Postfix, in my
> > configuration, rejects some emails. For example, from the Birmingham
> > Zoo, bto.org, etc. so I get an email in the morning with the rejections
> > of the day before and if I want to I add them in sender_access. In 1.5
> > years I have 14 domains there.
> > 
> > When time allows, I will add the DKIM rejections as well, based on your
> > case. Just in case. So thanks for sharing. I wonder if DKIM is rejecting
> > some "legit" (or "expected") email.
> > 
> 
> Sounds very useful, something you can share or is it top secret?

Nothing top secret. It's not a public script because I have it in a repo
with internal tools for the personal server.

What I have detects the emails rejected by "Client host rejected: cannot
find your reverse hostname" and "Client host rejected: cannot find your
hostname".

This is the script that parses the Postfix logs for those errors:
https://gist.github.com/cpina/e97c0da58f42a0db83b3886674de4410

I call (from cron) it from this Bash script:
https://gist.github.com/cpina/79b4f425facb6b97aaea4c572307de3a

The email looks like this:
https://gist.github.com/cpina/4c49df824742c5ae1d273170939795be

The reason that I wrote it was, as I said, I set up postfix to reject
emails based on the hostname (it reduced Spam) but some, very few
services, have the email set up in a way that is wrong. Then I can see
them and I add them in sender_access in Postfix.

What I will do, some day, is make sure that emails rejected because of
DMARC, are also there. So, if I expected an email from britishgas or
whoever and it appears in the morning email the day after, I would know
faster. Not ideal, but email seems full of not-ideal things :-)

Cheers,

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