SMTP Checker - Test Your SMTP Server Online
Your app says the email was sent - but nothing ever arrives, and nothing shows up in the logs. This free SMTP checker finds out why: enter your server details and it runs a live connection test with a real mail submission, verifying your SMTP host, port, credentials, and TLS security in seconds. Use it as an online SMTP tester before deployment, after a provider migration, or any time deliveries silently stop - no installation, no signup.
How to Test Your SMTP Server Settings
Setting up a WordPress plugin, a CRM, or an application that sends transactional email? Run this SMTP test to confirm your settings before you deploy.
- SMTP Server: Enter your server address (e.g., smtp.gmail.com or mail.yourdomain.com) - or pick a provider shortcut. The tool pre-fills settings for Gmail, Outlook, Yahoo, Sendgrid, Mailgun, SMTP2GO, Sendinblue, JangoSMTP, and GMass.
- Port: Choose your SMTP port - 587 for STARTTLS or 465 for implicit SSL in most setups. One-tap shortcuts cover 25, 2525, 465, and 587.
- Authentication: Enter the username and password from your email service provider to check SMTP credentials. Leave both blank to test an unauthenticated connection.
- Security: Select your encryption type. Most modern servers use STARTTLS on port 587. Leave it on "Auto" and the tool detects the correct security protocol from your port.
- From / To: Set the sender address and the inbox that should receive the test message.
- Start Test: Click "Start Test" to run the SMTP connection test and view the diagnostic log.
What is SMTP and Why Do You Need an SMTP Test Tool?
SMTP (Simple Mail Transfer Protocol) is the universal language servers use to send and relay emails across the internet. While it sounds simple, a single incorrect character in your configuration can lead to "silent" failures where emails are never sent. An online SMTP tester is essential for:
- Developers: Debugging application code that isn't sending mail.
- IT admins: Confirming firewalls aren't blocking outgoing mail ports and running a quick SMTP server test after configuration changes.
- SaaS users: Verifying credentials for third-party platforms like SendGrid, Mailgun, or Amazon SES.
SMTP Ports: Which One Should You Use?
Choosing the right port is the #1 reason for connection timeouts. Use this Port information as a quick reference for your email server test.
- 587 (STARTTLS): Modern Standard. Use this for almost all mail submissions.
- 465 (Implicit SSL/TLS): Secure Alternative. Used by Gmail and many legacy systems.
- 2525 (STARTTLS): The Fallback. Use this if your ISP blocks port 587.
- 25 (None): Avoid. Usually blocked by cloud providers (AWS/GCP) to prevent spam.
Common SMTP Errors and How to Fix Them
When you test your SMTP server, our tool may return specific error codes. Here is what they mean:
- 535 Authentication Failed: Your username or password is incorrect. Note: For Gmail/Outlook, you often need an "App Password" rather than your main account password.
- Connection Timeout: This usually means your hosting provider or ISP is blocking the port (often Port 25 or 587). Try switching to Port 2525.
- 550 Relay Denied: The server recognizes you but doesn't have permission to send mail to that specific recipient. Check your "From" email address.