About The SMTP Debug Tool

This professional and free-of-charge service allows you to test your SMTP connection, identify and fix possible sending issues in 3 different ways.

Check your SMTP connection and see the full SMTP session log to resolve any email-sending concerns. Check the connection to Amazon SES, SendGrid, Mailgun, Sendinblue, Google SMTP, Elastic Email, SMTP2GO, UniOne, or any other SMTP server.

  • Works with all existing SMTP providers
  • Real-time logs of the session
  • Available without logging in
  • Secure and easy-to-use

Tool Instructions


Define which of the tool’s options fits your needs the best

“SMTP Test” for a quick check-up, “SMTP Proxy” for debugging specific SMTP sessions, or “SMTP Blackhole” for the most protected test.


Go to the page of the chosen service:


Follow the instructions on the page of each specific tool

Read them carefully, and do not hesitate to Contact Us if you need assistance


Get access to “More Parameters” by signing in

Use extra fields in SMTP Test and reduce the limits in SMTP Proxy and SMTP Blackhole for extended and more comfortable testing of your SMTP server connection.

Frequently Asked Questions

Sending numerous emails may sometimes be quite a tricky thing. Checking your SMTP server operation may help you prevent possible deliverability issues and ensure that all of your emails reach their recipients. Using the SMTP Debug Tool is also a great way to learn the inner workings of the SMTP protocol.

The Tool establishes an SMTP session based on the provided parameters and sends a free test email. After that, it shows you the entire log of the “conversation” between servers, so that you can check if everything has gone right or if any problems need to be fixed.

Non-logged-in users can specify values for all the required fields: “Email From” and “Email To” addresses, Host, Port number, Username, and Password. For other fields, placeholders will be used.

If you sign in, you will be able to specify your own “Subject”, “HTML Body”, and additional email header fields, so you can test the contents of the letter as well.

Please note that the maximum length of a header name is 75 bytes, and it should contain only ASCII symbols, while the header value should not exceed 4000 bytes and it can include any UTF-8 symbols.

After inserting all the necessary data and pressing the “Send” button, you will see the session status at the top of the page (above the form), which may be one of the following:

  • “Email sent successfully. Click here to see the debug log.” - this means that your session has already been terminated, and you may view the complete log via the link (and also just below the form)
  • “Failed to send an email. Click here to see the debug log.” - sending failed due to some issues which took place during the session, and you may find out what exactly went wrong by clicking the link or scrolling down to see the comments.
  • “Invalid ____ (field name). Please try again.” - you’ll see this message if something is wrong with the value you’ve entered in the specific field. Double-check the information you’ve entered and retry.

Yes, we guarantee you that this is absolutely safe as both your connection to our site and the SMTP session are encrypted, and we do not keep the session log or any of the information you enter. Also, you may change your password after completing the tests to keep the highest level of privacy. Plus, you may use the “SMTP Blackhole” Tool without entering your credentials for maximum security.

Our SMTP Debug Tool is entirely free of charge.

However, we are a responsible company that fully respects spam prevention policies. That’s why we put certain restrictions on the number of requests. For SMTP Test:

  • no more than 10 sessions per hour for non-logged-in users
  • no more than 30 sessions per hour for logged-in users.

For SMTP Proxy tools:

  • no more than 2 sessions per hour for non-logged-in users
  • no more than 30 sessions per hour for logged-in users.

We believe the SMTP Debug Tool is one of the most complete and comfortable web-based SMTP testing tools because of the following advantages:

  • 3-in-1 complex service covering different needs in checking SMTP connection as no other else on the web
  • Free access to all essential functions without the need to log in
  • Allows you to specify any port number, including non-standard ones
  • Provides an opportunity to test the email session thoroughly by specifying “From Name”, and “To Name”, entering the “Subject” and the email content, and even up to 2 additional SMTP headers (available for the logged-in users)
  • Takes care of the safety and security of sensitive data
  • Helps to find out possible issues in existing SMTP sessions with any mailing service
  • User-friendly interface, clear and easy to use.

Please ensure you’ve followed all the instructions and haven’t reached the hourly limits (mentioned above).

If everything looks correct, but the session still hasn’t started, feel free to request assistance via the form in the “Contact Us” section.