How do international ISPs share spam reputation data?

International ISPs share spam reputation data through industry groups, shared blocklists, and informal networks. Organizations like M3AAWG (Messaging, Malware, and Mobile Anti-Abuse Working Group) facilitate information sharing about emerging threats and abusive senders.

Major blocklist operators aggregate reports from multiple sources, creating shared reputation that affects senders globally. When spam originating from your infrastructure hits multiple providers, they may independently report to shared resources, compounding reputation damage.

This interconnected reputation ecosystem means that problems anywhere can affect delivery everywhere. Maintaining good practices consistently matters because bad behavior gets shared. Conversely, building positive reputation with major providers often improves delivery to smaller ones through indirect trust signals.