[exim] Failed DKIM without selector

Hi,

i use dual DKIm sign with RSA and ED25519 keys (the selectors are named
with "r" and "e" at start respectively, to distinguish them).

Recently i enabled receiving DMARC reports and i see from google (i
didn't get from others yet), that the that RSA signatures passes and
ED25519 DKIM signatures fails:

    <auth_results>
      <dkim>
        <domain>mydomain.tld</domain>
        <result>pass</result>
        <selector>r2021</selector>
      </dkim>
      <dkim>
        <domain>mydomain.tld</domain>
        <result>fail</result>
        <selector>e2021</selector>
      </dkim>
    </auth_results>

I guess, that google doesn't supports ED25519 signatures yet, but that
is not problem, i have verified with some other provider, that it works.

The problem is, that some reports are failed with empty selector:

    <auth_results>
      <dkim>
        <domain>mydomain.tld</domain>
        <result>pass</result>
        <selector>r2021</selector>
      </dkim>
      <dkim>
        <domain>mydomain.tld</domain>
        <result>fail</result>
        <selector></selector>
      </dkim>
    </auth_results>

As here is not selector, i can guess only, that it is the ED25519
(because the RSA one pass).

I have setup DKIM (debian based):

  DKIM_DOMAIN         = ${domain:$h_from:}
  DKIM_SELECTOR       = ${lookup{$dkim_domain} lsearch{DKIMDBFILE}}
  DKIM_PRIVATE_KEY    = ${lookup {$dkim_selector.$dkim_domain.key} \
                          search{CONFDIR/dkim}{CONFDIR/dkim/$value}}

In DKIMDBFILE i have mapped selectors based on domain, eg:

mydomain.tld: r2021:e2021

My question is, please, how i can log outgoing DKIM-Signature header(s)
to be sure, that i am not sending empty selector? As they are not all
messages, i do not know which one fails with empty selector (if any),
thus i want to log them all (for some time).

regards

--
Slavko
http://slavino.sk