How do ISPs, ESPs, and blocklists communicate?

Communication happens through multiple channels. Feedback loops let MBPs report spam complaints directly to ESPs. Blocklists publish real-time query interfaces (DNSBL) that receiving servers check during mail processing. Industry forums like M3AAWG enable direct relationships between players.

Postmaster teams at major MBPs maintain relationships with legitimate high-volume senders. ESPs cultivate these relationships to resolve delivery issues and stay informed about policy changes. Blocklist operators provide delisting processes and sometimes direct communication channels.

Much communication is automated: DNSBL queries happen programmatically, feedback loop reports arrive via standardized ARF format, and DMARC reports flow through email. Human communication focuses on escalations, policy discussions, and emerging threat coordination. Both layers are essential.