Since yesterday evening, all our mail servers seem to have been blacklisted on the same DNSBL: spam.dnsbl.anonmails.de.
But after a quick verification it turns out that this DNSBL has disappeared and is no more.
In this case it's enough to remove this DNSBL from your monitoring - in our case it's check_rbl from Matteo Corti. A relevant pull request was created on the upstream project.
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