SMTP Tester

Debug email delivery issues. Test connection, authentication, and SSL/TLS security with real-time logs.

SMTP Host

The address of your mail server.

Port

Common ports: 25, 465 (SSL), 587 (TLS).

Use Secure Connection (SSL/TLS)

Enable if your server requires encryption. Recommended for Port 465/587.

Use Authentication

Enable if you need to provide a username and password.

Credentials

Username

Password

From Email

Must often match the authenticated user.

To Email

Where the test email will be sent.

What is SMTP and Why Test It?

SMTP (Simple Mail Transfer Protocol) is the backbone of email delivery on the internet. It handles the sending of messages from an email client to a mail server, and then to the recipient's server.

Configuring SMTP correctly is crucial for ensuring your emails—whether transactional alerts, newsletters, or personal messages—actually reach the inbox and don't end up in spam folders or getting blocked entirely. Our SMTP Tester helps you verify your settings without needing to install complex local software.

Common SMTP Ports Explained

Port 25 (Legacy): The original standard for moving mail between servers. Most residential ISPs and cloud providers block this port to prevent spam. Avoid using it for submission.
Port 587 (Submission): The standard secure port for submitting mail. It supports STARTTLS, which upgrades an insecure connection to a secure one. This is the recommended port for most modern applications.
Port 465 (SMTPS): Uses Implicit SSL, meaning the connection is secure from the start. While technically deprecated, it is still widely supported by services like Gmail and Outlook.
Port 2525 (Alternative): Often used as a fallback when port 587 is blocked by firewalls.

Troubleshooting Common Errors

If your test fails, check the Transaction Log for these common codes:

535 Authentication Failed

Your username or password is incorrect. If using Gmail, you likely need to enable 2-Factor Authentication and generate an App Password instead of using your main login.

550 Relay Access Denied

The server refused to send the email. This often happens if you try to send mail without authentication, or if the "From" address doesn't match the authenticated domain.

Connection Timed Out

The server is unreachable. Check if your hosting provider blocks outbound SMTP traffic (common on AWS, DigitalOcean) or if you have a firewall rule blocking the port.

Security Best Practices

Always use encryption (SSL/TLS) when connecting to an SMTP server. Sending credentials in plain text over Port 25 makes them vulnerable to interception. Our tool supports both explicit (STARTTLS) and implicit SSL modes to help you verify secure connections.