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SMTP Tester

SMTP Tester Tool

Diagnose email issues instantly with SMTP Tester.
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💡 Pro tip: Common SMTP ports are 25 (standard), 465 (SSL), and 587 (TLS). Most providers recommend using port 587 with TLS encryption for sending emails.
🪙 Cost: 1 token

The Free Online SMTP Tester is designed to verify and troubleshoot your email server functionality. You can easily connect to your server by entering either the server name or IP address in our simple interface. The tool allows you to specify both sender and recipient email addresses to simulate a complete email transaction, providing clear insights into whether your SMTP server is functioning correctly.

This diagnostic tool is particularly valuable for developers and system administrators who need to identify and resolve email delivery issues. By revealing exactly what’s happening during the SMTP connection process, you can quickly pinpoint configuration problems or connectivity issues. Once these problems are addressed, your email server will be able to reliably deliver messages to their intended recipients.

Our SMTP Tester provides a complete view of the entire communication process between your email client and the server, helping you ensure that your email infrastructure is properly configured and operating efficiently.

Frequently Asked Questions

An SMTP (Simple Mail Transfer Protocol) Tester is a diagnostic tool that helps verify your email server configuration by establishing a test connection and simulating the sending of an email. You might need one when setting up a new email server, troubleshooting delivery issues, or confirming that your email service provider is functioning correctly. Our SMTP Tester shows the exact conversation between your client and the mail server, helping identify configuration errors, authentication problems, or connectivity issues that prevent emails from being delivered.
Yes, our SMTP Tester is designed with security as a priority. We use encrypted connections (HTTPS) for all web traffic, never store your credentials or email content on our servers, and process all testing data in-memory only. Your credentials are used solely for the purpose of authenticating with your mail server during the test and are immediately discarded after the test completes. We also implement automatic session timeouts to provide additional security. However, for additional peace of mind, we recommend creating temporary application-specific passwords when testing services that offer this feature.
SMTP response codes are three-digit numbers that indicate the status of each command in the SMTP conversation. The first digit generally indicates the category: 2xx codes indicate success (e.g., 250 OK), 3xx codes indicate the server is ready for additional information, 4xx codes indicate temporary failures that may succeed if retried later, 5xx codes indicate permanent failures. Some common specific codes include: 220: Server ready for SMTP conversation, 235: Authentication successful, 354: Start mail input, 421: Service not available, 450: Mailbox unavailable (temporary), 550: Requested action not taken (often means invalid recipient), 554: Transaction failed. Our SMTP Tester provides plain-language explanations alongside these codes to help you understand what they mean in context.
Authentication failures (typically error 535) can occur for several reasons: Incorrect username or password - Double-check for typos and ensure you're using the full email address when required. Security settings - Some providers like Gmail require you to enable "Less secure apps" or create an app-specific password. Account restrictions - Your account may have restrictions preventing third-party access. Two-factor authentication - If you have 2FA enabled, you'll need to use an app password instead of your regular password. IP restrictions - Some servers only accept connections from specific IP addresses. Our SMTP Tester provides detailed error messages that can help pinpoint the specific authentication issue you're experiencing.
Viewing the complete SMTP conversation provides several benefits: It shows exactly where in the process a failure occurs It reveals server-specific error messages that may contain helpful troubleshooting information It helps identify timing issues or unexpected server behaviors It can expose problems with specific commands or responses It provides confirmation that all parts of the conversation are working as expected This level of detail is especially valuable for system administrators, developers implementing email functionality, or anyone diagnosing complex email delivery issues.

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