What is the meaning of "callout=unknown" in the callout db? What could
produce that cached output?
> $ sudo exim_dumpdb /var/spool/exim4 callout |grep -v @ |grep lists
> 07-May-2018 10:14:47 lists.example.fr callout=unknown
> postmaster=unknown random=unknown
I had to reduce "callout_domain_negative_expire" to 0s, because
otherwise, messages sent to our listserver are sometimes rejected by our
MTA Exim, and cached for 3h ("result of an earlier callout reused").
I struggle to find out why Exim thinks that, sometimes, messages to this
domain should be rejected.
