smtp-test

SMTP Test Tool | Check Email Server Configuration Online

Free online SMTP tester to verify SMTP connections, test mail servers, and diagnose email delivery issues. Perfect for Gmail, Office 365, SendGrid, and custom SMTP servers.

SMTP Configuration

Enter your SMTP server details
Common ports:

Enable to send a test email after successful connection

Your SMTP credentials are never stored and are only used temporarily for testing

Terminal Output

Idle
SMTP connection logs will appear here
$ Ready to test SMTP connection...

Popular SMTP Server Settings

Quick reference guide for common email providers

Gmail SMTP Test

Host:
smtp.gmail.com
Port:
587
Security:
STARTTLS

Requires App Password if 2FA enabled

Microsoft 365 SMTP

Host:
smtp.office365.com
Port:
587
Security:
STARTTLS

Use your full email as username

Amazon SES SMTP

Host:
email-smtp.[region].amazonaws.com
Port:
587
Security:
TLS

Requires SMTP credentials from AWS

SendGrid SMTP Relay

Host:
smtp.sendgrid.net
Port:
587
Security:
TLS

Use API key as password

Understanding SMTP Testing and Verification

A comprehensive guide to testing SMTP servers and email configurations

Why Use an SMTP Test Tool?

Our SMTP test utility helps verify email server configurations before deploying to production. Whether you need to test SMTP connections, check SMTP server settings, or validate your SMTP relay setup, this tool provides comprehensive diagnostics for your email infrastructure.

Server Verification

  • SMTP server test validation
  • Connection security checks
  • Authentication verification
  • Port accessibility testing

Relay Testing

  • SMTP relay configuration
  • Mail server routing
  • Message delivery verification
  • Transport layer security

Benefits of Regular SMTP Testing

Using an SMTP checker regularly helps maintain email system reliability. Our SMTP testing tool provides real-time diagnostics, helping identify common issues like authentication failures, connection timeouts, or relay access problems. Whether you're setting up a new mail server or maintaining existing infrastructure, regular SMTP checks ensure optimal email delivery performance.

Key Features of Our SMTP Test Utility

  • Comprehensive SMTP connection testing
  • Real-time server response monitoring
  • Detailed diagnostic reporting
  • Support for various SMTP configurations
  • Instant feedback on server settings

SMTP Troubleshooting FAQ

Find answers to common questions about the SMTP Test Tool.

What ports should I use for SMTP?

Common SMTP ports are:

  • Port 25: Default SMTP port (often blocked by ISPs)
  • Port 465: SMTP over SSL/TLS
  • Port 587: SMTP with STARTTLS (recommended)

Which security option should I choose?

  • Auto: Let the tool detect the security type (recommended)
  • SSL/TLS: Use encrypted connection from start (usually port 465)
  • STARTTLS: Start unencrypted, then upgrade to TLS (usually port 587)
  • None: No encryption (not recommended for production)

Are my SMTP credentials secure?

Yes. Your credentials are never stored and are only used temporarily to run the SMTP test. The entire process is secure and ephemeral. All data is discarded after the test completes.

What happens during the test?

The tool will:

  1. Try to connect to your SMTP server
  2. Attempt authentication if credentials are provided
  3. Verify SMTP commands work correctly
  4. Send a test email if that option is enabled

You'll see the full SMTP conversation in real-time in the terminal window.

What do common SMTP error messages mean?

  • Connection refused: Server is down or port is blocked
  • Authentication failed: Invalid username/password
  • Relay access denied: Server won't forward emails
  • Timeout: Server took too long to respond (25 seconds)
  • Invalid recipient: Email address not accepted

How do I fix SMTP authentication errors?

Common authentication issues and solutions:

  • Verify username format (some servers require full email, others just username)
  • Check if app-specific password is required (common with Gmail, Microsoft 365)
  • Ensure 2FA is properly configured if enabled
  • Confirm the correct port and security settings are selected

Which email providers can I test with this tool?

This SMTP tester works with all major email providers including:

  • Gmail SMTP (smtp.gmail.com)
  • Microsoft 365 / Office 365 (smtp.office365.com)
  • Amazon SES SMTP
  • SendGrid SMTP
  • Custom email servers and self-hosted solutions

What are SMTP relay servers and when should I use them?

SMTP relay servers are intermediary servers that handle email delivery for you. Use one when you send high volumes from an application, need better deliverability and inbox placement, want to avoid running your own mail infrastructure, or need delivery analytics. Popular relay services include SendGrid, Amazon SES, Mailgun, and Postmark.

How can I improve email deliverability?

To improve email delivery rates:

  • Set up SPF, DKIM, and DMARC records for your domain
  • Use dedicated IP addresses for sending emails
  • Ensure proper reverse DNS (PTR) records are configured
  • Monitor sender reputation and blacklist status
  • Follow email best practices and CAN-SPAM guidelines

What's the difference between SMTP and API-based email services?

  • SMTP: Standard email protocol, widely supported but older technology
  • API-based: Modern REST APIs, often easier to implement and maintain
  • SMTP: More firewall-friendly, uses standard ports (25, 465, 587)
  • API-based: Better error handling and real-time feedback
  • Both: Can be used for transactional and marketing emails

SMTP Testing Resources & Guides

SMTP Test Online

Test SMTP connections online instantly with our free browser-based tool

SMTP Checker

Verify email server configuration and validate SMTP settings

SMTP Test Tool

Professional SMTP testing tool with advanced diagnostics

How to Test SMTP

Complete guide on testing SMTP servers and email configurations

SMTP Troubleshooting

Fix common SMTP errors and email server issues

Email Validator

Verify email format, check syntax, and detect disposable addresses

Email Header Analyzer

Parse headers, trace routes, and check SPF/DKIM/DMARC

MX Lookup

Find the mail servers for a domain, their priority, IPs and email provider

SPF Record Checker

Validate an SPF record, count DNS lookups and expand every include

SPF Record Generator

Build a valid SPF record for Google Workspace, Microsoft 365, SES and more

DMARC Record Checker

Look up and explain a domain's DMARC policy, reporting and alignment

DMARC Record Generator

Create a DMARC TXT record with policy, reports and alignment settings

DKIM Record Checker

Check a DKIM selector, read the public key and its length, or scan common selectors

All Free Email Tools

Every SMTP, DNS and email authentication tool in one place