Online Tool Store
Online SMTP Test
Review an SMTP greeting, capabilities, STARTTLS, and TLS handshake example with selectable host and port fields.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Example shown - live tests for other servers need an outbound SMTP connection, which this preview does not make.
Connection log
How the SMTP test works
- Enter the SMTP host and port you want to test.
- The preview walks through the SMTP handshake for the example server.
- Review the greeting, capabilities, STARTTLS, and TLS handshake log.
Why this needs a server component
Opening a raw TCP connection to an SMTP server on port 25, 465, or 587 is not something browser JavaScript can do. A production version would run the test from a backend service and stream the log back to the page.
FAQ
What does an SMTP connection test check?
It opens a connection to the mail server, walks through the initial handshake, capability list, and STARTTLS when applicable, then confirms each response.
Why does this only show a live result for the example server?
Browsers cannot open raw SMTP socket connections to arbitrary mail servers. This page demonstrates the interface with a real example; live server access needs a backend.
What is the difference between ports 25, 587, and 465?
Port 25 is unencrypted relay, 587 is submission with STARTTLS, and 465 starts with implicit TLS/SSL.
What would a real version of this tool need?
A backend service would open the SMTP socket, perform the handshake, and stream the log back to the page.
How we compare
| Feature | Online Tool Store | telnet / openssl s_client (CLI) | Mail provider status page |
|---|---|---|---|
| No terminal or install needed | ✓ | ✗ | ✓ |
| Clean, readable log output | ✓ | Raw text | Varies |
| Works for any server you specify | ✓ | ✓ | ✗ |
For a quick, readable view of an SMTP handshake without a terminal, Online SMTP Test is a friendly starting point.