SMTP Tester

Debug your email server configuration. Connect, authenticate, and send a test email to verify your SMTP settings.

SMTP Host

host or ip address of your smtp server (example: smtp.gmail.com)

Port

the default port is 25, but some smtp servers use a custom port (example: 587 or 465)

Use Secured Connection Use authentication

checked it only if the smtp server needs a secured connection (ssl, tls)
most of smtp servers need an authentication (login/password). Check it if required

required if 'Use authentication' is checked (ex: account or account@foo.com)

Password

required if 'Use authentication' is checked

Email from

the sender's email address (example: account@foo.com)

Email to

very important : the test mail will be sent to this address (ex: account@foo.com)

Test your mail server

What is SMTP and How Does an SMTP Tester Help?

SMTP (Simple Mail Transfer Protocol) is the standard communication protocol used to send email messages across the internet. It is the "postman" of the digital world, responsible for routing emails from your mail client (like Outlook or Apple Mail) or web application to the recipient's mail server.

Configuring SMTP servers can be complex. Issues with firewalls, incorrect ports, authentication failures, or SSL/TLS handshakes are common. An SMTP Tester Tool is essential for developers, network administrators, and digital marketers to verify that their email infrastructure is working correctly before deploying it to production environments.

Why Test Your SMTP Server?

Verify Connectivity: Ensure your server can physically reach the SMTP host (e.g., `smtp.gmail.com`) without being blocked by a firewall.
Check Authentication: Confirm that your username (usually an email address) and password (or App Password) are accepted by the server.
Debug TLS/SSL: Validate that the secure handshake (STARTTLS) works correctly to encrypt your emails.
Test Deliverability: Prove that the server actually accepts and queues the email for delivery to the final recipient.

Understanding Common SMTP Ports

Choosing the correct port is the most common stumbling block when configuring SMTP. Here is a breakdown of the standard ports used:

Port 25 (Standard / Relay)

This is the original standard port for SMTP. It is primarily used for server-to-server relaying. However, most residential ISPs (Internet Service Providers) and cloud hosting providers (like AWS EC2, Google Cloud) block Port 25 by default to prevent spam. Do not use this port for email submission in modern apps unless you explicitly know it's required.

Port 587 (Modern Submission)

This is the standard port for mail submission by mail clients and web applications. It supports explicit SSL (STARTTLS), meaning the connection starts insecurely and then upgrades to a secure connection. This is the recommended port for services like SendGrid, Mailgun, and Outlook.

Port 465 (Implicit SSL)

This port connects using Implicit SSL, meaning the connection is encrypted from the very first byte. While technically deprecated by the IETF in favor of STARTTLS, it is still widely used and supported by major providers like Gmail (Google Workspace) and many shared hosting cPanels.

Port 2525 (Alternative)

This is not an official standard port, but many email service providers (like SendGrid and Postmark) support it as an alternative to Port 587. It is useful when Port 587 is blocked by a strict firewall.

How to Debug SMTP Errors

Our tool provides a detailed Transaction Log. Here is how to interpret common errors you might see:

Connection Timed Out / Failed to Connect: This usually means a firewall is blocking the connection, or the hostname is incorrect. Ensure your server allows outbound traffic on the port you selected.
535 Authentication Failed: The username or password is incorrect. Note: If you are using Gmail, your regular password won't work. You must enable 2-Factor Authentication and generate an App Password.
550 Relay Access Denied: This happens if you try to send mail without authentication, or if the "From" address is not authorized for your account (common with strict SPF policies).
Certificate Verify Failed: The server's SSL certificate is invalid, expired, or self-signed. You may need to disable "Secure Connection" or fix the certificate on the mail server.

SMTP Security: SSL vs TLS vs STARTTLS

Security is non-negotiable for email. Sending emails in plain text puts passwords and sensitive data at risk.

SSL (Secure Sockets Layer) is the older technology, now largely replaced by TLS (Transport Layer Security). However, the terms are often used interchangeably. STARTTLS is a command used to upgrade a plain text connection to a secure TLS connection. Our tool supports both modes: checking "Use Secured Connection" will attempt to negotiate the highest level of security supported by the server.

Conclusion

Stop guessing why your emails aren't sending. Use our Free SMTP Tester to get instant feedback and detailed logs. Whether you are setting up a WordPress site, configuring a CRM, or coding a custom application, this tool gives you the confidence that your email pipeline is solid.