How do you test relay authentication?

You're about to start sending campaigns through a relay service, and the last thing you want is to waste your sender reputation by using bad credentials or wrong settings. Testing relay authentication before you go live is how you catch these mistakes safely.

The easiest method is swaks (Swiss Army Knife for SMTP). This command-line tool walks through the full authentication handshake and tells you exactly what went wrong if something's broken. Your command looks like this: swaks to test@example.com from you@yourdomain.com server smtp.relay.com:587 auth auth-user your_username auth-password your_password tls. You'll see every step of the connection, whether encryption worked, and whether the server accepted your credentials.

If you prefer a more manual approach, you can use openssl to connect directly and type SMTP commands yourself. Run: openssl s_client -starttls smtp -connect smtp.relay.com:587. Then type EHLO yourdomain.com, then AUTH LOGIN, then your base64-encoded username and password. The server will respond with success or an error code that points you to the problem. It's more work than swaks but teaches you how SMTP authentication actually works.

For a quicker test without command-line tools, set up the relay in an email client like Outlook or Thunderbird and send a test message. If it fails, check the client's error message and your relay's logs.

Common mistakes worth checking. Port 587 uses STARTTLS (starts unencrypted, then upgrades to TLS); port 465 uses full encryption from the start. Wrong port is the most common error. Your username might need to be formatted differently.sometimes it's your email, sometimes it's just your account ID. Passwords with special characters need URL encoding. Some relays require app-specific passwords or two-factor authentication. Check your relay's documentation for these details.

So Your next step is to test with swaks first. It'll tell you exactly which setting is broken, and you can fix it before you touch your production sending setup.