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You can test mySMTP connectivity and authentication directly from the terminal before integrating it into an application. Use swaks for quick tests, OpenSSL for TLS inspection, and telnet or PowerShell for port verification.

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Prerequisites

  • Your mySMTP username and password from the setup email
  • Your mySMTP hostname from the setup email (shown as relayxx.mysmtp.com in these examples)
  • swaks, OpenSSL, or telnet installed on your system

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Test with swaks

swaks is a command-line SMTP testing tool that handles authentication and TLS automatically.

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Install swaks

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Send a test email

Replace relayxx.mysmtp.com, YOUR_USERNAME, and YOUR_PASSWORD with your real hostname and credentials from the setup email.

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Test TLS with OpenSSL

Use OpenSSL to inspect the TLS handshake and send a manual SMTP session.

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STARTTLS on port 587

After the TLS handshake completes, start the SMTP session:
The server responds with 334 VXNlcm5hbWU6, which is the Base64 prompt for username. Encode your username and password in Base64:
Paste each encoded string at the prompt. Then send the message:

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Implicit TLS on port 465

After the handshake, use the same SMTP commands as above.

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Verify port reachability

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Windows (PowerShell)

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Linux and macOS (telnet)

If the connection succeeds, you see an SMTP greeting like 220 relayxx.mysmtp.com ESMTP. Type QUIT to close. If the connection times out, the port is blocked by a firewall or ISP.

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Linux and macOS (nc)

Never paste real passwords into shared terminals or log files. Use test credentials or a dedicated test account when possible.

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Automated online testing

Run a full deliverability and authentication test at test.smtp.ai. It checks port connectivity, TLS negotiation, authentication, and DNS records in one step.
After confirming the connection works, verify your domain authentication with the mySMTP Deliverability Toolbox. It includes 19 free tools including SPF validation and sender readiness checks.

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Common errors

Your username or password is incorrect, or your account is not yet activated. Re-enter credentials exactly as shown in the setup email. See Setting up SMTP credentials.
Your network or host may block port 587. Try port 2525 with the same swaks command, or port 465 with OpenSSL. See Supported SMTP ports and encryption.
The OpenSSL flags do not match the port. Use -starttls smtp for ports 587 and 2525. Use -connect without -starttls for port 465.