Subscription Bombing: COI, CAPTCHA, and the Next Generation of Mail Bombs

Spamhaus observed an automated mail‑bombing campaign beginning on August 12 in which bots submitted large volumes of subscriptions and account signups across many web forms (including Single Opt-In and some Confirmed Opt-In lists), causing confirmation and credential emails to overwhelm recipients and providers. The attackers likely used scripts to harvest signup endpoints and submit addresses at scale; Spamhaus mitigated the incident by listing IP addresses from major sources and warns this may be an emerging Mail‑bombing-as‑a‑Service offering.