@1358531 @mcc BSI emails owner of the IP range, owner of the IP range looks up if they can match the IP to a customer (i.e. it's a statically assigned one and not a dynamic pool) and if they can they email the customer "hey your server has this weird open port/resolver/..., could you please check on that, and fix it if it is actually a problem?"
(I got such a mail in the past, but can't find it and can't 100% say if it was based on a BSI report or just something the provider noticed themselves)