The @postalsys/bounce‑classifier library is a lightweight, pure‑JavaScript machine‑learning model that reads the human‑readable diagnostic text of SMTP bounce messages and assigns each to one of 16 predefined categories, each mapped to a concrete remediation action (e.g., remove, retry, fix configuration). It runs entirely client‑side—usable in Node.js or in browsers—so no API calls or data leave your infrastructure, making it ideal for high‑volume, privacy‑sensitive email pipelines that need automated, actionable bounce handling.