SMTP Debug Tool
Test and debug your SMTP connection. Quickly and for free.
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A free web tool to test, proxy, and blackhole SMTP connections with real-time session logs.
- for
- Developers and engineers who need to debug email sending setups.
- pricing
- free
Key features
- SMTP Test — Run a quick SMTP session in the browser and view the full conversation log.
- SMTP Proxy — Log an existing SMTP connection between your app and mail provider for error analysis.
- SMTP Blackhole — Create a safe test session without exposing real credentials, capturing logs only.
- Real-time logs — See live, detailed logs of every SMTP command and response.
- No login required — All core functions are accessible without registration.
- Extended parameters for logged-in users — Add subject, HTML body, and extra headers, and raise hourly limits.
Use cases
- Verify that a new email service (e.g., SendGrid) is configured correctly before production.
- Debug intermittent delivery failures by proxying the live SMTP traffic of an app.
- Test email templates and headers safely using the blackhole mode without sending real mail.
SMTP Debug Tool FAQ
Why should I use the SMTP Debug Tool?+
It helps you detect deliverability issues and understand SMTP protocol behavior before sending real emails.
How does the SMTP Test work?+
It creates an SMTP session with the supplied parameters, sends a test email, and displays the complete server conversation log.
Is it safe to enter my SMTP username and password?+
Yes, connections are encrypted, logs are not stored, and you can change passwords afterward; the Blackhole mode requires no credentials.
How many free SMTP sessions can I run?+
Non-logged-in users get up to 10 test sessions and 2 proxy sessions per hour; logged-in users get up to 30 of each per hour.
What makes this tool different from others?+
It combines three functions—Test, Proxy, and Blackhole—into one free, browser-based service with no login required.
Summarized by DevHunt from smtpdebug.com · Sep 28, 2026. Details may change; check the official site.
