How do ESPs detect spoofed senders?

ESPs verify that senders control claimed domains through authentication setup requirements. Before allowing sending from your domain, ESPs require DNS record configuration proving domain ownership.

Ongoing verification includes: comparing sending patterns against expected behavior, monitoring for sudden changes suggesting compromise, and checking authentication consistency across messages.

Abuse detection systems flag suspicious activity: new accounts sending high volumes, content patterns matching known spam campaigns, and authentication configurations that appear designed to deceive. These systems protect ESP reputation by preventing abuse.