@stefano @ErikJonker @secretsquirrel Blocking all IPs of offending ASNs is the only effective remedy I think.
@stefano @ErikJonker @secretsquirrel Given the reactions I've polished a small tool that I created a while ago for this purpose. There are some known ASNs in there and the resulting IP ranges, but careful using this on IP level for a system that handles email: https://codeberg.org/sdassow/asn-blocks