Free SMTP ToolPut the debugger between your app and your real SMTP provider. Your software sees normal SMTP, while you see both sides of every command and reply, clearly tagged by direction as they happen.
The debugger sits between both systems and records each command, response, status code, and error in the order it was received, giving you a clear view of the entire SMTP session from connection through delivery attempt.
Instead of relying on application logs or simplified error messages, you can see exactly how your software communicated with the provider and where the interaction started to fail.
This makes it easier to diagnose authentication problems, TLS issues, rejected senders or recipients, malformed commands, provider restrictions, rate limits, and other SMTP errors that are otherwise difficult to trace.
FAQHow the SMTP proxy works, how your provider credentials are handled, and how to follow both sides of the SMTP conversation.
An SMTP proxy debugger sits between your application and your real SMTP provider. It forwards the SMTP session normally while showing you every command and response exchanged between both sides in real time.
Only the SMTP host and credentials used by your application need to change temporarily. Your application still connects using standard SMTP, so no code changes should normally be required.
Yes. The debugger connects to the SMTP provider you configure and relays the session between your application and that provider. Messages are still submitted through your actual SMTP service.
Your provider credentials are used to establish the upstream SMTP connection for the debugging session. They should only be retained for as long as necessary to operate that session and should not appear in the transcript.
You can see SMTP commands and responses from both your application and your provider, including connection setup, EHLO, authentication, MAIL FROM, RCPT TO, DATA, errors, and delivery responses.
The debugger labels each entry so you can tell whether it came from your application, the debugger, or your SMTP provider. This makes it easier to follow the SMTP conversation and identify where a failure occurs.
Yes. The proxy can handle normal SMTP connections, including encrypted SMTP sessions and authentication, depending on the connection settings you configure.
The temporary SMTP endpoint stops accepting connections. Create a new debugging session if you need to continue testing.
Yes. Because you can see the SMTP provider's exact responses, the debugger can help identify authentication failures, rejected recipients, TLS problems, sender restrictions, rate limits, and other SMTP errors.
No. It shows you what happens during the SMTP transaction, but it does not change how receiving mail servers treat your messages. It is primarily a troubleshooting tool for SMTP connections, commands, responses, and provider errors.
Free, no signup required, and each tool shows you the exact response from your mail server so you can see the full details.
FeaturesEverything behind reliable delivery at any volume: sending, verification, routing, and the analytics to see what happened, from first API call to millions a month.
Send transactional and bulk emails through reliable SMTP infrastructure built for speed, security, and deliverability.
Integrate email delivery into your applications using powerful APIs built for flexibility, scalability, and performance.
Separate transactional and marketing traffic into isolated sending streams to protect reputation and keep critical emails fast.
Receive and route incoming emails directly into your applications using flexible automation and processing workflows.
Create and deliver marketing campaigns designed to increase engagement, reach, and customer retention.
Receive real-time event notifications for deliveries, opens, and clicks for storage and automation workflows.
Monitor email performance with detailed insights, reporting tools, and actionable delivery metrics in real time.
Gain greater sending control with dedicated IPs designed for consistency, reputation, scalability, and reliability.
Build integrations faster using SDKs, code examples, and resources for modern application development.
