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Free Tool

SMTP Tester

Verify SMTP connectivity, TLS negotiation, and auth in seconds—no account required.

Enter the SMTP server hostname or IP address.

Common ports: 25, 465 (SMTPS), 587 (STARTTLS).

Timeout between 1000 and 30000 ms.

Optional hostname sent during the EHLO/HELO command.

Choose either Secure or STARTTLS. Require TLS will fail if TLS is not established.

Tests the connection, TLS negotiation, and optional auth. Results are returned as JSON for troubleshooting.

FAQ

SMTP Tester FAQs

Answers to common questions about SMTP testing and credentials.

Does this tool send any emails?

No. It only tests the SMTP handshake, TLS, and optional authentication.

Are my credentials stored?

No. Credentials are only used to perform the test and are not stored.

When should I use STARTTLS vs SMTPS?

Use STARTTLS for ports like 587, and SMTPS for implicit TLS ports like 465.

How this SMTP tester works

  1. Enter your SMTP host and port.
  2. Choose TLS options and add credentials if needed.
  3. Run the test to see the handshake, capabilities, and auth results.

When to use it

  • Before switching ESPs or SMTP relays.
  • When TLS or auth settings fail in your sending app.
  • To confirm STARTTLS support on port 587.