17 SMTP Tools to Diagnose and Test Email Security

Sending emails is a crucial part of business communication. For emails to reach their intended recipients, a properly configured and secured SMTP server is essential. However, issues like misconfigurations, vulnerabilities, and spam filters can prevent your emails from getting delivered.

This is where SMTP testing and diagnostic tools come in. These tools can identify issues with your SMTP server and email security, troubleshoot problems, and help improve deliverability.

In this comprehensive guide, we will explore the best 17 SMTP testing tools to diagnose and test the security of your email server.

What is SMTP?

Before getting into the tools, let‘s first understand what SMTP is.

SMTP stands for Simple Mail Transfer Protocol. It is the standard protocol used for sending emails across the internet.

When you send an email from your email client or app, the email is handed over to your company‘s SMTP server. This server then communicates with the recipient‘s SMTP server using the SMTP protocol to deliver the email.

Some key things to know about SMTP:

• SMTP is only used for sending and relaying emails. Protocols like IMAP and POP3 are used to receive emails.

• Each mail server has an SMTP server that handles outgoing emails. Popular SMTP servers include Exchange, Postfix, Sendmail, etc.

• The default SMTP port is 25. However, SMTP connections can also be made over SSL/TLS on port 587 or 465.

• SMTP uses TCP as the underlying transport protocol.

Why Test Your SMTP Server?

There are several reasons why you should periodically test and diagnose the health of your SMTP server:

• Identify misconfigurations – SMTP testing can reveal misconfigured DNS records, incorrect ports, authentication issues, etc. rectify con problems.

• Check security – Tools can check for open relays, spoofing, SSL configuration, and other vulnerabilities. This improves email security.

• Troubleshoot delivery issues – Diagnosing SMTP connections can help troubleshoot and fix email delivery failures.

• Reduce bounces – Testing can lower bounce rates by detecting issues before sending bulk emails.

• Improve deliverability – A healthy SMTP server leads to fewer emails ending up in spam or not reaching recipients.

Overall, testing provides insight into the workings of your SMTP server and helps build an efficient email delivery infrastructure.

Next, let‘s explore some of the best SMTP testing and diagnostic tools available.

17 Useful SMTP Testing Tools

1. SocketLabs

SocketLabs offers a free SMTP testing and diagnostics tool.

It allows you to test and troubleshoot connections to your SMTP server. The tool supports both secure (SSL) and non-secure server connections.

It contains a library of SMTP commands like EHLO, MAIL FROM, RCPT TO, DATA, etc. that it can use for testing.

SocketLabs is a lightweight tool that you can download and run on Windows machines with .NET Framework 2.0 or later.

2. MxToolbox

MxToolbox is another popular SMTP diagnostic tool.

You just need to enter your mail server‘s address and click the Test SMTP Server button.

It will connect to your mail server using SMTP and perform an Open Relay Test. This checks if your server has a valid reverse DNS (PTR record).

You can also use MxToolbox to evaluate response times for your mail server. If you don‘t know your mail server address, you can do an MX Lookup using this tool.

3. Wormly

Wormly‘s SMTP test allows you to validate email addresses on your server.

Enter your SMTP server‘s IP or domain name. Also provide an email address to verify whether that address is recognized by your SMTP server via the RCPT TO command.

There is also an option to override the default TCP port used by your SMTP server. You can choose to send a test email or just do an SMTP handshake test.

4. CheckTLS

CheckTLS offers a free email security assessment tool.

Their EmailSentry Outlook addon ensures your sent emails are private, compliant, and secure.

It can detect issues with your email security and provide one-click fixes. CheckTLS is compliant with regulations including HIPAA, GDPR, CCPA, and PCI.

5. SSL-Tools

SSL-Tools has a simple SMTP server test tool.

You just need to enter your domain name, without the email address, to check the security of your incoming mail server.

It will examine if the server supports STARTTLS encryption and has a valid SSL certificate. SSL configuration issues like Heartbleed vulnerability are also tested.

6. ImmuniWeb

ImmuniWeb offers a free online SMTP security test.

It can check your mail server, web server, SSL certificates, and compliance with standards like PCI DSS.

ImmuniWeb has already performed over 73 million security tests, making it a reliable tool.

Just enter your mail server‘s address and start the free SMTP test. For more detailed reports, you can upgrade to their paid plans.

7. DNSQueries

DNSQueries has an SMTP server health checker tool.

It first tries to connect to your specified mail server. Then it attempts to send a test email via that server.

If both tests are successful, it indicates your SMTP server is configured properly.

You just need to enter your hostname and click Check. It is one of the simplest online SMTP testing tools.

8. SMTPTester

SMTPTester is an open-source command-line SMTP testing tool.

It is written in Python and tests for three common vulnerabilities:

• Spoofing – Sender address spoofing
• User Enumeration – Validating user accounts through VRFY command
• Open Relay – Unauthorized mail relaying

Install Python and run SMTPTester to diagnose these security issues in your mail server. You can specify ‘internal‘, ‘external‘ or ‘vrfy‘ as arguments to test for a specific vulnerability.

9. Header Analyzer

As the name suggests, Message Header Analyzer allows you to inspect email headers.

Paste the full message header and it will break it down into a readable format.

You can analyze headers to identify security issues, trace email paths, troubleshoot delivery problems and more.

10. Microsoft Remote Connectivity Analyzer

Microsoft offers an Exchange Server Connectivity Analyzer
tool.

It has specific tests for checking inbound and outbound SMTP connectivity issues.

The inbound SMTP test shows you how an external email passes through different stages to reach your mail server.

Similarly, the outbound test checks aspects like reverse DNS, Sender ID, and RBL list checks for your outgoing IPs.

11. NetScanTools Pro

NetScanTools Pro has a robust SMTP diagnostics suite. It includes:

A. SMTP Email Generator

This tool lets you generate and send emails via an SMTP server for testing purposes. You can set custom headers, attach files, use SMTP auth, etc.

It also captures the communication between the SMTP server and the tool for in-depth analysis.

B. SMTP Relay Testing

It performs over 15 different relay tests to identify open relays and other SMTP vulnerabilities.

You can select the specific relay tests you want and view detailed logs in text or HTML format.

12. SMTPPing

SMTPPing is a simple, cross-platform CLI tool for checking SMTP server response times.

It measures the delay, throughput, and connection variability when connecting to your SMTP server. This helps identify any latency issues.

13. Mailpit

Mailpit is a developer-friendly email testing tool.

It is written in Go language and offers an installation-free SMTP server and web interface for testing emails.

Mailpit supports SMTP relaying, HTML email rendering, HTTPS, basic auth, and more. It also provides official Docker images.

14. MailHog

MailHog is another developer-centric email testing tool.

It is built with Go and lets you configure your application to send emails to it for testing instead of actual mail servers.

These emails can then be viewed in MailHog‘s web interface. It also allows forwarding emails to real SMTP servers.

MailHog is customizable with storage options, release rules, Chaos Monkey, and more.

15. LunaticSMTP

LunaticSMTP is an extensible fake SMTP server for testing.

It is developed in Java and provides a GUI web interface.

LunaticSMTP offers advanced capabilities like mail autoresponders, address rewriting, throttling, etc.

Note that it requires JavaFX and Java 11+ to run.

16. MailDev

MailDev simplifies email testing for developers with its easy web interface.

It allows resizing the viewport for responsive testing. MailDev also exposes a RestAPI for managing messages programmatically.

As it is built on Node.js, you get the advantage of JavaScript on both client and server sides.

17. Mailocal

Mailocal provides a local SMTP server and testing interface using PHP.

The setup only takes a single composer command. You can even configure a custom database by passing the appropriate DSN URL.

Overall, Mailocal makes it easy to create a stable SMTP testing environment with its simple installation process.

How to Use SMTP Testing Tools

Now that you know about various SMTP testing tools, let‘s go through the general process of using them:

1. Identify Your SMTP Server Details

First, gather details like the SMTP server IP address, host name, admin email accounts, etc.

Your email service or IT team should be able to provide these.

2. Select a Suitable Tool

Go through the list of tools above and pick one that suits your requirements, budget, and technical expertise.

3. Configure the Tool

Perform any installation or configuration steps required for the tool. For online tools, you can directly start testing.

4. Run SMTP Tests

Use your SMTP details to execute a set of tests. Refer to the tool‘s documentation for specifics.

5. Analyze Results

Analyze the test results and logs to identify any vulnerabilities, misconfigurations, latency issues and more.

6. Retest After Fixing Issues

For any problems found, fix the underlying issue in your SMTP setup. Confirm by retesting with the same tool.

7. Schedule Periodic Testing

Configure tests to run automatically at scheduled intervals to catch any new issues proactively.

Tips for Effective SMTP Testing

Here are some tips to maximize the effectiveness of your SMTP testing efforts:

• Test with and without authentication to uncover different vulnerabilities.

• Check open relay vulnerabilities from both internal and external networks.

• Use multiple test tools as they may detect different issues.

• Compare results before and after making server changes.

• Test connectivity with valid and invalid mailboxes on your domain.

• Ensure TLS security, DNS settings, reverse DNS, SPF, and DKIM are configured properly.

• Set up monitoring to track SMTP server performance over time.

• Analyze SMTP error logs on your mail server for clues.

• Ensure spam filters are not too restrictive by testing with known good emails.

• Check deliverability to free webmail services to confirm public delivery.

FAQs About SMTP Testing

Q. What does an SMTP test check?

SMTP testing tools check aspects like:

• Encryption and certificate validation
• Authentication and authorization
• DNS records and reverse DNS
• Ability to relay emails
• Protection against protocol attacks
• Valid mailboxes on the domain
• Latency and throughput

Q. How often should I test SMTP?

Ideally, you should test your core SMTP infrastructure once a month. Also test after every major server upgrade, DNS change, or configuration change.

For deliverability, sample test emails should be sent to free webmail accounts weekly or fortnightly.

Q. Does SMTP testing send real emails?

Most SMTP test tools only simulate sending emails and do not actually deliver emails to others. But some tools have the option to send real test mails to check end-to-end deliverability.

Q. Can SMTP testing be automated?

Yes, many SMTP testing tools support automation through command-line usage, APIs, and schedulers. This allows you to run diagnostics on a regular basis automatically.

Monitoring tools can also continuously measure SMTP performance metrics.

Conclusion

We looked at 17 useful SMTP testing and diagnostic tools like SocketLabs, MxToolbox, MailHog, Mailpit, etc.

These tools can reveal vulnerabilities in your email infrastructure, troubleshoot delivery issues, and help improve security and deliverability.

I hope this guide gives you a good understanding of how to thoroughly test your SMTP server. Let me know in the comments if you have any other favorite SMTP testing tools I should check out!