What is SMTP and why do I need to test it?

SMTP (Simple Mail Transfer Protocol) is the standard protocol for sending emails across the internet. Testing your SMTP configuration ensures your email server can properly authenticate, establish secure connections, and deliver messages. This is critical before deploying email functionality in applications or when troubleshooting delivery failures.

What's the difference between port 25, 587, and 465?

Port 25 is the traditional SMTP port but is often blocked by ISPs for security reasons. Port 587 (STARTTLS) is the recommended submission port that upgrades connections to encrypted after initial connection. Port 465 (implicit TLS) establishes encryption immediately. Modern servers typically use port 587 or 465 for secure authenticated connections.

Why am I getting an authentication failed error?

Authentication failures typically result from incorrect email credentials, unsupported authentication methods, or special characters in passwords requiring encoding. Verify your username and password are correct, ensure your account has SMTP access enabled, and check if your server requires specific authentication protocols like PLAIN or LOGIN.

How do I know if my firewall is blocking SMTP connections?

If your SMTP test times out or shows connection refused errors, your firewall likely blocks outbound SMTP traffic. Contact your network administrator to open the necessary SMTP port (25, 587, or 465) in your firewall rules. You can also test from different networks to confirm if the issue is network-specific.

Can I use SMTP Test to send actual emails?

Yes, SMTP Test can send real emails to verify your server configuration. The test establishes a genuine SMTP connection and delivers the message through your actual mail server. This confirms not only that your settings are correct but also that the entire email delivery pipeline functions properly end-to-end.

SMTP Test

How to Use SMTP Test

When to Use SMTP Test

Technical Information

Frequently Asked Questions