SMTP Server Test Tool
Test SMTP server connection and configuration. Verify SMTP settings, authentication, and email delivery.
Test SMTP Connection
SMTP Server Configuration
Authentication (Optional)
Test Email
Test Results
Connection Details
Privacy & Security Notice
Important: This tool is for testing purposes only. Your SMTP credentials are transmitted securely but we recommend using test credentials when possible. No credentials or email data are stored on our servers. All tests are performed in real-time and logs are not saved.
What is SMTP?
SMTP (Simple Mail Transfer Protocol) is the standard communication protocol for sending emails across the Internet. It defines how email messages are transmitted from a client (such as your email application) to a mail server, and from one mail server to another.
When you send an email, your email client connects to an SMTP server, authenticates (if required), and transmits the message. The SMTP server then routes the email to the recipient's mail server using DNS lookups and additional SMTP connections.
How to Use the SMTP Test Tool
- Select a Provider: Choose from popular SMTP providers or select "Custom SMTP Server" to manually enter your settings.
- Enter SMTP Host: Provide the hostname or IP address of your SMTP server (e.g., smtp.gmail.com).
- Configure Port & Security: Select the appropriate port (587 for TLS, 465 for SSL) and encryption method.
- Add Credentials: Enter your SMTP username and password if authentication is required.
- Set Email Addresses: Specify the sender (From) and recipient (To) email addresses for the test.
- Test Connection: Click "Test SMTP Connection" to initiate the test and view the SMTP conversation log.
Common SMTP Ports Explained
Port 587 (Recommended)
Use: TLS encryption (STARTTLS)
This is the modern standard for email submission. It starts with an unencrypted connection and upgrades to TLS encryption. Supported by most email providers.
Port 465
Use: SSL encryption (SMTPS)
Uses SSL/TLS from the start of the connection. Originally deprecated but now widely used for secure SMTP connections.
Port 25
Use: No encryption (Legacy)
Traditional SMTP port without encryption. Often blocked by ISPs to prevent spam. Not recommended for client-to-server communication.
Port 2525
Use: Alternative port
Alternative to port 587 when it's blocked. Commonly used by email service providers as a backup submission port.
Popular SMTP Providers
| Provider | SMTP Server | Port | Security |
|---|---|---|---|
| Gmail | smtp.gmail.com | 587 / 465 | TLS / SSL |
| Outlook/Office365 | smtp.office365.com | 587 | TLS |
| SendGrid | smtp.sendgrid.net | 587 / 465 | TLS / SSL |
| Mailgun | smtp.mailgun.org | 587 / 465 | TLS / SSL |
| Amazon SES | email-smtp.region.amazonaws.com | 587 / 465 | TLS / SSL |
Common SMTP Errors & Solutions
Connection Timeout
Cause: Firewall blocking the SMTP port or incorrect server address.
Solution: Verify the SMTP server address and port. Check if your firewall or ISP is blocking the port. Try alternative ports (2525 instead of 587).
Authentication Failed (535 Error)
Cause: Incorrect username or password.
Solution: Verify your credentials. For Gmail, ensure you're using an App Password if 2FA is enabled. For Office365, use your full email address as username.
TLS/SSL Handshake Failed
Cause: Incorrect encryption method or outdated SSL/TLS protocol.
Solution: Match the encryption method to the port (TLS for 587, SSL for 465). Ensure your server supports modern TLS versions.
Relay Access Denied (550 Error)
Cause: SMTP server doesn't allow relaying for your IP or email address.
Solution: Enable SMTP authentication and use valid credentials. Ensure your "From" email address is authorized on the SMTP server.
Frequently Asked Questions
Is this tool safe to use with my real SMTP credentials?
Yes. All connections are encrypted (HTTPS), and we don't store any credentials or logs. However, for maximum security, we recommend using test credentials when possible.
Will this tool actually send an email?
No. This tool only tests the connection and authentication with your SMTP server. It simulates the email sending process but doesn't actually deliver a message.
Why can't I connect to Gmail SMTP?
Gmail requires an App Password if you have 2-factor authentication enabled. Also, "Less secure app access" must be enabled for accounts without 2FA. We recommend using App Passwords.
What does the SMTP conversation log show?
The log displays the actual SMTP protocol commands and responses between the client and server. This helps diagnose exactly where a connection might be failing.
Can I test SMTP servers on custom ports?
Yes. The port field allows any valid port number. Simply select your desired port from the dropdown or enter a custom value.
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