SMTP Server Test
Test mail server connectivity, verify SMTP authentication, check TLS support, and troubleshoot email delivery issues. Essential for email administrators and developers.
Test SMTP Server
Quick Tests:
💡 Testing Tips
• Port 587 is recommended for modern email clients (STARTTLS)
• Port 465 uses SSL/TLS from the start (SMTPS)
• Port 25 may be blocked by ISPs for residential connections
• Connection failures may indicate firewall blocks or server issues
• TLS support is essential for secure email transmission
What We Test
🔌 Connectivity
Verify the server accepts connections on standard SMTP ports (25, 587, 465).
⏱️ Response Time
Measure connection speed and server responsiveness for performance monitoring.
🔒 TLS Support
Check if the server supports STARTTLS or SSL/TLS encryption for secure communication.
🎯 SMTP Banner
Display server greeting message and identify mail server software.
Common SMTP Ports
Port 25 - Standard SMTP
Traditional SMTP port for server-to-server communication. Often blocked by ISPs.
Port 587 - Submission (Recommended)
Modern standard for client email submission with STARTTLS encryption.
Port 465 - SMTPS
SMTP over SSL/TLS. Deprecated but still widely used by email clients.
Troubleshooting Tips
- Verify server hostname and port number
- Check firewall rules and port blocking
- Test from different networks to isolate issues
- Confirm authentication credentials if required
- Check server logs for error messages
- Verify DNS MX records point to correct server
SMTP Commands Reference
Basic Commands
Extended greeting and capability inquiry
Close connection
Security Commands
Upgrade to encrypted connection
Authenticate with username/password
Plain text authentication (base64)
Frequently Asked Questions
What is SMTP and why test it?
SMTP (Simple Mail Transfer Protocol) is the standard protocol for sending emails. Testing SMTP servers helps verify connectivity, authentication, TLS support, and troubleshoot email delivery issues before they affect your users.
What SMTP ports should I test?
Common SMTP ports: Port 25 (standard SMTP), Port 587 (submission with STARTTLS), Port 465 (SMTP over SSL/TLS). Port 587 is recommended for client submissions, while port 25 is used for server-to-server communication.
Why is my SMTP connection failing?
Common causes: firewall blocking ports, incorrect server settings, authentication failures, TLS/SSL issues, or the server being offline. Check server hostname, port, credentials, and security settings.
What is SMTP authentication?
SMTP authentication (SMTP AUTH) requires username/password verification before allowing email sending. This prevents unauthorized use of mail servers and is essential for preventing spam and securing email systems.
How do I troubleshoot SMTP timeouts?
SMTP timeouts usually indicate network issues, firewall blocks, or server overload. Check firewall rules, verify server is running, test from different networks, and ensure correct port numbers.
What is STARTTLS vs SSL/TLS?
STARTTLS upgrades a plain connection to encrypted (port 587), while SSL/TLS uses encryption from start (port 465). STARTTLS is more flexible and commonly preferred for modern email clients.