Free Online SMTP Test - Check Email Server & SMTP Connection

Online SMTP Test – Check Your Email Server Instantly

The Online SMTP Test by the Academy of Digital Marketing (ADM) is a free and reliable tool designed to help you verify, diagnose, and troubleshoot SMTP (Simple Mail Transfer Protocol) server connections quickly and efficiently.

This tool allows you to test whether your email server is correctly configured and functioning as expected. It checks critical elements such as SMTP authentication, relay permissions, server connectivity, and response time. With just a few inputs, you can identify email delivery issues before they impact your communication or campaigns.

Whether you are facing email delivery failures, authentication errors, slow sending speeds, or server misconfigurations, the Online SMTP Test provides a fast and accurate way to pinpoint the problem and take corrective action.

What Is SMTP?

SMTP (Simple Mail Transfer Protocol) is the standard protocol used to send emails over the internet. It is responsible for routing outgoing emails from the sender’s email client or application to the recipient’s mail server.

In a typical email workflow:

• SMTP handles sending emails
• IMAP or POP3 handle receiving emails

SMTP servers authenticate the sender, relay messages between servers, and ensure emails are delivered to the correct destination. If any part of this process fails, emails may not be sent, may bounce back, or may be delayed.

Key Features of the Online SMTP Test Tool

Instant SMTP Server Check

The Online SMTP Test allows you to instantly test whether your SMTP server is reachable and responding correctly. With a single test, you can confirm server connectivity and ensure your email infrastructure is online and operational.

Authentication & Relay Verification

The tool verifies whether your SMTP credentials are correct and checks if the server allows authenticated email relaying. This helps detect common issues such as incorrect usernames, passwords, or blocked relays that prevent emails from being sent.

Troubleshoot Email Delivery Issues

If emails are failing to send, bouncing back, or getting delayed, the SMTP Test helps identify the root cause. It detects problems related to server misconfigurations, authentication failures, relay restrictions, and potential blacklisting issues.

Verify SMTP Ports (25, 465, 587)

Different SMTP ports are used for different encryption methods. The tool checks whether your server is correctly configured to send emails using:

• Port 25 for standard SMTP
• Port 465 for SSL encryption
• Port 587 for TLS encryption

This ensures secure and reliable email transmission.

Real-Time SMTP Response Logs

The tool provides detailed, real-time response logs from the SMTP server. These logs show each step of the email handshake process, making it easier to diagnose errors and understand exactly where the problem occurs.

Supports All Major Email Providers

The Online SMTP Test works seamlessly with popular email services such as Gmail, Outlook, Yahoo, Zoho Mail, as well as custom and private SMTP servers. This makes it suitable for businesses, developers, and marketers using any email setup.

No Setup Required

The tool runs entirely online and requires no software installation or technical configuration. Simply enter your SMTP details and run the test.

Free & Secure Testing

The SMTP Test is completely free to use and does not store or track your credentials. All checks are performed securely and in real time.

How to Use the Online SMTP Test Tool

Testing your email server’s SMTP settings with the ADM Online SMTP Test Tool is quick and straightforward. You don’t need advanced technical knowledge—just your SMTP details. Follow these steps:

Step 1: Enter SMTP Server Details

Start by entering your SMTP server hostname in the input field. This is usually provided by your email service provider.

Examples:

• smtp.gmail.com
• smtp.office365.com
• smtp.zoho.com
• Your custom mail server hostname

This allows the tool to connect to the correct email server.

Step 2: Choose the SMTP Port

Select the appropriate SMTP port based on your email provider and security requirements:

• Port 25 – Standard SMTP
  Used for basic SMTP connections, but often blocked by ISPs to prevent spam.
• Port 465 – SMTP with SSL Encryption
  Used for secure email transmission with SSL encryption.
• Port 587 – SMTP with STARTTLS Encryption (Recommended)
  The most commonly recommended port for secure and reliable email sending.

Choosing the correct port is critical for successful email delivery.

Step 3: Enter Authentication Details (If Required)

Many SMTP servers require authentication to prevent unauthorised email sending.

If required, enter:

• SMTP username
• SMTP password

These credentials verify your identity and allow the server to relay emails securely.

Step 4: Run the SMTP Test

Click the “Test SMTP” button to start the process. The tool will attempt to:

• Connect to the SMTP server
• Authenticate the credentials
• Verify relay permissions
• Test email sending capability

All checks are performed in real time.

Step 5: Analyse the Results

Once the test is complete, you’ll see detailed SMTP response logs. These logs help you understand:

• Whether the connection was successful
• If authentication failed
• If the server blocked email relaying
• Any configuration or security issues

Use this information to fix errors and optimise your SMTP setup.

Why Use the SMTP Test Before Sending Emails?

Running an SMTP test before launching email campaigns or activating transactional emails helps you detect and fix issues early—before they affect customers, leads, or internal communication.

An SMTP test helps prevent common problems such as:

• Email delivery failures
• Contact form submission issues
• SMTP authentication errors
• Missed customer communications
• Delayed or bounced transactional emails

By testing your SMTP setup in advance, you can ensure your email system is reliable, secure, and ready for use.

Why Use an SMTP Test?

Fix Email Sending Issues

SMTP tests help identify server-level misconfigurations that prevent emails from being sent. These may include incorrect hostnames, wrong ports, invalid credentials, or relay restrictions. Detecting these issues early saves time and avoids campaign failures.

Ensure Email Server Security

An SMTP test verifies whether authentication and encryption (SSL/TLS) are correctly configured. This ensures that only authorised users can send emails and protects your server from misuse or security breaches.

Improve Email Deliverability

Email providers closely monitor SMTP behaviour. Misconfigured servers can cause emails to be blocked, rejected, or flagged as spam. Testing your SMTP setup helps ensure smooth email transmission and better inbox placement.

Check Firewall & ISP Restrictions

Some ISPs and firewalls block certain SMTP ports, especially port 25. An SMTP test helps you determine whether network restrictions are preventing successful email connections and whether alternative ports should be used.

Validate SMTP Authentication

Many email servers require proper authentication before allowing emails to be sent. An SMTP test confirms that your username and password are valid and that your server allows secure, authenticated email relaying.

Common SMTP Errors & How to Fix Them

SMTP errors usually indicate problems with server availability, authentication, configuration, or recipient details. Understanding these errors helps you resolve email delivery issues quickly.

421 – Service Not Available

What it means:
The mail server is temporarily unavailable. This often happens due to server overload, maintenance, or network connectivity issues.

How to fix it:

• Restart the mail server
• Check internet and network connectivity
• Verify firewall and hosting provider restrictions
• Try sending emails again after some time

450 – Mailbox Unavailable

What it means:
The recipient’s mailbox is temporarily unavailable or busy. The email server could not deliver the message at that moment.

How to fix it:

• Verify the recipient’s email address
• Check if the recipient server is online
• Retry sending the email later
• Ensure your SMTP server is not rate-limited

451 – Server Error

What it means:
A temporary server-side error occurred, often related to DNS issues or incorrect server configuration.

How to fix it:

• Check DNS records (MX, SPF, DKIM)
• Review SMTP server configuration
• Restart the email service
• Contact your email hosting provider if the issue persists

550 – Message Rejected

What it means:
The email was rejected by the recipient’s server. This usually happens when the email address does not exist or the domain is invalid.

How to fix it:

• Confirm that the recipient email address is correct
• Validate the email address before sending
• Ensure your sending domain is not blacklisted
• Check SPF, DKIM, and DMARC records

535 – Authentication Failed

What it means:
The SMTP server rejected the login credentials. This is one of the most common SMTP errors.

How to fix it:

• Verify SMTP username and password
• Ensure authentication is enabled
• Check SSL/TLS encryption settings
• Use the correct SMTP port (usually 465 or 587)
• Regenerate app passwords if required (Gmail, Outlook, etc.)

Conclusion

The Online SMTP Test by the Academy of Digital Marketing is an essential diagnostic tool for website owners, email marketers, developers, and IT professionals. It helps you quickly identify SMTP configuration issues, authentication errors, and server-level problems that can disrupt email delivery.

By testing your SMTP setup in real time, you can:

• Prevent email delivery failures
• Fix contact form and transactional email issues
• Improve email reliability and deliverability
• Ensure secure and correctly configured email servers

Run an SMTP test now to diagnose issues early and improve your email communication efficiency with confidence.

Frequently Asked Questions

1. What does an SMTP test do?

An SMTP test checks whether your mail server can successfully send emails. It verifies server connectivity, authentication credentials, SMTP ports, encryption settings, and identifies any errors that may prevent email delivery.

2. How do I know if my SMTP server is working?

You can use the Online SMTP Test to check if your server is reachable and correctly configured. The tool shows real-time connection status and response logs. If the test fails, the error message helps you fix the issue.

3. Can I test SMTP without authentication?

Some SMTP servers allow unauthenticated relaying, but most modern email providers require authentication using a username and password to prevent spam and misuse. For best security and deliverability, authenticated SMTP is recommended.

4. What are the most common SMTP ports?

The most commonly used SMTP ports are:

• Port 25 – Standard SMTP (often blocked by ISPs)
• Port 465 – SMTP with SSL encryption
• Port 587 – SMTP with STARTTLS encryption (recommended)

5. Why is port 587 recommended for SMTP?

Port 587 supports STARTTLS encryption and is widely accepted by email providers. It offers better security and fewer delivery issues compared to port 25.

6. What information do I need to run an SMTP test?

You typically need:

• SMTP server hostname
• SMTP port number
• Username and password (if authentication is required)
• Encryption type (SSL or TLS)

7. Can this tool help fix contact form email issues?

Yes. If your website contact form emails are not being delivered, the SMTP test can help identify authentication errors, blocked ports, or server misconfigurations.

8. Does the SMTP test send a real email?

The tool simulates the email sending process and checks server responses. It verifies whether your SMTP server can send emails without affecting your actual inbox or users.

9. Is the Online SMTP Test tool free to use?

Yes. The Academy of Digital Marketing’s Online SMTP Test is completely free and does not require registration or subscriptions.

10. Is my SMTP login information safe?

Yes. The tool does not store or save your credentials. All SMTP tests are performed securely and in real time.

11. Can I use this tool with Gmail or Outlook SMTP?

Yes. The tool supports popular email providers such as Gmail, Outlook, Yahoo, Zoho Mail, and custom or private SMTP servers.

12. What does an SMTP authentication failed error mean?

This error usually indicates incorrect login credentials, disabled authentication, or incorrect encryption or port settings. Double-check your username, password, and SMTP configuration.

13. Why are my emails going to spam even if SMTP works?

SMTP tests confirm server functionality, but spam issues are often related to missing SPF, DKIM, or DMARC records. You should also check email content and sender reputation.

14. Should I run an SMTP test after server changes?

Yes. Always run an SMTP test after changing hosting providers, updating server settings, migrating websites, or modifying email configurations.

15. Who should use the Online SMTP Test tool?

This tool is ideal for:

• Website owners
• Email marketers
• Developers
• System administrators
• Businesses sending transactional emails