Online SMTP Tester for Email Debugging
Use our free online SMTP tester to verify email server connections, test authentication, and debug delivery issues instantly. Test your SMTP setup now.
SMTP Validator
Test and debug your SMTP server configurations.
Server Configuration
Enter your SMTP details below.
Enable for port 465
Send Test Email
Debug Log
About SMTP Tester
The SMTP Tester allows developers and system administrators to verify connection parameters, validate server authentication, and troubleshoot email routing without installing specialized local diagnostic software.
Running directly in your browser, this tool helps you isolate configuration bugs for libraries like Nodemailer and cloud relays like AWS SES, SendGrid, or Google Workspace. It is entirely free and requires no account signup.
Key features
- Test SSL, TLS, and STARTTLS encrypted connections
- Verify custom SMTP hostnames and port configurations
- Validate username and password authentication mechanisms
- Send test messages to verify actual inbox delivery
- Inspect raw server handshakes and SMTP error codes
- Troubleshoot configuration issues for frameworks like Nodemailer
How to use SMTP Tester
- Enter your mail server hostname and destination port.
- Select the required encryption protocol, such as TLS or STARTTLS.
- Enter authentication credentials if your server requires login.
- Specify sender and recipient email addresses for the test dispatch.
- Click Run Test to review server handshakes and response status codes.
Who is it for?
- Developers debugging mail delivery in Node.js, Python, or PHP applications.
- DevOps engineers checking firewall policies and open outbound mail ports.
- System administrators validating credentials for Microsoft 365 or Google Workspace.
- QA testers confirming transactional notification delivery in staging environments.
Frequently asked questions
What is an SMTP tester?
An SMTP tester is a diagnostic utility that connects to an email server to confirm that the hostname, port, security protocols, and credentials work properly.
Which ports should I use for SMTP testing?
Port 587 is standard for modern email submission with STARTTLS. Port 465 is typically used for implicit SSL/TLS encryption, while port 25 is primarily reserved for server-to-server relay.
Why is my SMTP connection timing out?
Timeouts usually happen because your hosting provider, firewall, or internet service provider blocks outbound traffic on ports 25, 465, or 587.
Can I use this tool to debug Nodemailer configurations?
Yes. You can test the exact host, port, secure flag, and auth credentials configured in your Nodemailer transport object to pinpoint the source of connection errors.
Are my SMTP credentials stored when running a test?
No. Your server credentials and test messages are processed exclusively to perform the connection request and are never saved or stored.