#rcptx

Smart, asynchronous SMTP reconnaissance and deliverability probing — without sending a single email.

GitHub Repository | Documentation | Latest Release

#What is it?

Sometimes you need to know if an email address is real: a mailing list full of dead addresses hurts your sender reputation, and "does [email protected] actually exist?" is a surprisingly common question. The usual way to find out is to send a message and see if it bounces.

rcptx takes a different route. It connects to the domain's mail server and performs the same handshake a mail sender does — right up to the step before an email would actually go out — and reads the server's yes/no answer for each address. The recipient never receives anything, and you get a clear verdict per address: exists, doesn't exist, can't tell, or the domain accepts everything (a "catch-all").

#What can it do?

• Verify addresses across one or many domains at once, using built-in name presets (hr, support, executive…) or your own candidate lists.
• Detect catch-all domains up front, so you don't waste time scanning a domain that says "yes" to everything.
• Map a domain's email setup: which mail provider actually handles its mail (Google Workspace, Microsoft 365, Proofpoint, and 40+ more), plus its SPF and DMARC records — all from DNS alone if you prefer zero SMTP traffic.
• Play nice: it reuses connections, paces itself with delays and jitter, and retries gracefully when a server greylists you — the polite defaults are on by default.
• Report cleanly: a readable table for humans, or JSON/CSV output for scripts, with filters like "only the addresses that exist".

#Who is it for?

For anyone doing legitimate deliverability work — cleaning subscriber lists before a campaign, checking your own domain's mail posture, or authorized security assessments. The README includes a clear ethical-use note: probe only domains you have a real reason to investigate. Prebuilt binaries are available for Linux, macOS, and Windows. Open source under MIT.