WHAT IS IT?
Check If Email Exists (aka Reacher) is a Rust library that verifies whether an email address is valid without ever sending an email. It chains syntax validation, DNS/MX resolution, SMTP connection and deliverability checks to give you a reachability score (safe/risky/invalid/unknown). Available as a Rust crate, a CLI tool, or a dockerized HTTP backend.
WHY IS IT INTERESTING?
- Full verification without sending: Syntax, DNS, MX, SMTP, catch-all, full mailboxes, disabled accounts - all without sending a single email
- Disposable email detection: Automatically identifies temporary addresses (Guerrilla Mail, Mailinator, etc.) and role accounts (info@, admin@)
- Three deployment modes: Rust crate you can embed in your code, CLI for scripting, or HTTP backend via Docker for a REST API
- Written in Rust: Fast and reliable, handles volume without breaking a sweat
- No telemetry: Self-hosted, your verification data stays with you
USE CASES
- Cleaning an email list before a campaign to reduce bounce rates
- Validating addresses at signup to prevent fake accounts
- Integrating email verification into a CI/CD pipeline or onboarding workflow
- Detecting disposable addresses to improve lead quality