[exim] How to enable incoming DKIM check, ideally in Ubuntu/Debian?

[Mario Emmenlauer via Exim-users]

Hi,

I'd like to reject emails that are not sent from a valid DKIM-enabled
sender. Previously, I enabled similar checks for SPF, reverse DNS,
sender verification, and even more, and found that there are numerous
sources on the web that help. But for DKIM, I could not really find
anything useful, or I'm lacking the right search terms.

My question is slightly specific to Ubuntu/Debian, so in case there
are some users that know which switches to flip on these distros, it's
even more welcome. But I'm also happy with general insight into DKIM
incoming email check.

I did find a guide that shows how to use SpamAssassin for this step.
But other sources indicated that plain exim is sufficient?

Thanks for any help!

All the best,

    Mario Emmenlauer

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