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In Security and Test Management Last updated: September 19, 2023
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Sending emails is an important part of your business.

It implies that you rely on your SMTP server; it’s something that most people do not usually care to think about.

Businesses emphasize creating lots of email copies and newsletters. Still, not everyone is actually concerned about testing your emails whether they have correct HTML, are free of mistakes, and deliver at the right place.

As a result, it can lead to errors, emails ending up in spam folders, weird formatting, and even failing to display properly in certain email clients. Businesses have lost their customers this way, or at least made their users disappointed.

So, what’s the solution?

To identify potential risks and fix the issues associated with your inbound and outbound emails, you need to think about the roots of these troubles.

And for that, SMTP testing tools can help you!

That’s right.

So, let’s find out more about an SMTP testing tool and why you need it.

What is an SMTP?

Simple Mail Transfer Protocol (SMTP) is a set of rules used while sending emails.

Usually, this protocol is associated with IMAP or POP3. However, SMTP is utilized to deliver messages, while POP3 and IMAP are utilized to receive them.

Please don’t confuse it with SMTP relay services, which are 3rd-party services or applications used while transferring emails between multiple servers, domains, and hosting services.

And SMTP servers are systems that are utilized to carry out just email delivery. Similarly, SMTP authentication refers to the identification process that ISP clients (such as Outlook Express) undergo with the mail server they use to send the emails.

What are the SMTP test tools?

An SMTP test tool can identify SMTP server issues and troubleshoot them to keep your email secure and safe.

For this, the tool sends the SMTP server a message, and then it displays and records the trials and results in a log. This message goes via the ISPs, and when the message gets authenticated with the associated password and username by the SMTP mail server, the connection is established.

But if the tool fails to make that connection, it will show you the results while helping you to solve the problems that failed in the first place.

It helps in many ways, and some of them are below.

Easy-to-detect and fix issues

The tools help you check what is wrong with your SMTP server by offering an easy to understand log details. It checks whether or not your login credentials are correct or there is any external threat.

Without this tool, you may not know the actual reason why your emails are not reaching the right destination. So, it also saves your efforts, time, and cost associated with sending every mail.

Integration support

Modern SMTP services come with lots of integration options, so you can leverage the tools you already use. It varies from one SMTP test tool to another, but common integrations are IPv6 support, SOCKS support, ICAP support, etc.

Reduces bounce rates

By ensuring that your email security system is safe, your email bounce rates would be reduced. It implies that email deliverability will be higher to bring your better conversion rates.

Next, let’s find out some of the best SMTP tools you can use to test and diagnose issues and maintain security.


SocketLabs offers a free tool for SMTP testing, diagnostics, and monitoring that is free to use and download. It helps you to test and troubleshoot SMTP connections.

The tool supports both secure (SSL) and open SMTP server connections. It contains an in-built library of commands like DATA, EHLO, RCPT TO, and more. This SMTP tool is lightweight to download and requires Windows & .NET 2.0 framework or higher.


Test and diagnose your server security with MxToolbox. All you need to do is enter your mail server address and hit the button next to the field.

This test connects your mail server through SMTP and performs an Open Relay Test. This way, the tool helps you verify if the server includes a reverse DNS or PTR record.

Apart from that, you can also calculate the response times associated with your mail server. In case you are not aware of your mail server’s address, you can consider taking up an MX Lookup.


Start an SMTP test from Wormly by entering your SMTP server IP or your full domain address. Enter your email address so the tool can verify your address with your SMTP server or with RCPT TO.

There is also an option to override your default TCP port of your SMTP server. You can also opt to send an SMTP test email over the given email address. Alternatively, you can choose “No” if you want to perform an SMTP handshake testing.


Using CheckTLS, you can check your email security and how your emails are working. Their EmailSentry Outlook helps you ensure all your sent emails are private, legal, and safe.

The tool is approved by HIPAA, CCPA, PCI, GDPR, and other compliance regulations for email security. On detecting any issues with your emails after the test, CheckTLS also helps you to fix them.


Check the encryption of your email server from the simple tool by SSL-Tools. It is a pretty straightforward tool to enter the domain part of an email address and test its security.

It will help you discover whether its incoming mail server supports STARTTLS and has an authentic SSL certificate or not. You can also find out about its Perfect Forward Secrecy in addition to testing their vulnerabilities to Heartbleed.


ImmuniWeb offers an efficient tool to test SSL security. It is a free tool that has performed 73M security tests already.

The various types of SSL security tests that the tool offers are for:

  • Email servers
  • Web servers
  • SSL certificates
  • Test for PCI DSS, NIST, and HIPAA

Just enter your mail server address or website and start testing.


DNSQueries provides a useful tool to help you check your SMTP server’s health to make sure everything is working correctly.

At first, the test tries connecting to your mail server and then sends mail via this. Next, it displays the result directly on this web page. If the tool is successful in doing both things, rest assured things are good.

Enter your hostname to get the test started.


A python-based tiny utility,  SMTPTester is a great tool that can test your SMTP mail server for three common vulnerabilities – spoofing, user enumeration, and relays.

Go ahead, install Python and SMTPTester to check if your SMTP server is vulnerable.

You have three options to consider for using the tool:

  • Internal – to test mail spoofing only
  • External – to test mail relay only
  • Vrfy – to test user enumeration only. If you don’t specify any specific test type, the tool performs both external and internal tests and then appends the results.

Header Analyzer

As the name suggests, this easy-to-use and simple tool – Message Header Analyzer helps you analyze your message headers for security. Just paste a message header that you wish to analyze and get the results directly. As simple as that!

Microsoft Analyzer

Microsoft Remote Connectivity Analyzer provides lots of tests, including tests for Inbound and outbound SMTP emails.

The Inbound SMTP Email test shows you the various steps taken by an email server to send your domain an inbound SMTP email. Similarly, an Outbound SMTP Email test finds out your outbound IPs for some requirements. It includes Reverse DNS, RBL checks, and Sender ID.


NetScanTools Pro SMTP Server Tests Tool is a 2-in-1 tool.

#1. SMTP Email Generator

It is designed to test the process of sending emails via an SMTP mail server. It gives you access to all the header parameters, such as to confirm for urgent flags.

It supports basic SMTP authentication or through STARTTLS with a password and username for the server that needs them. The tool lets you send attachments via mail, log email sessions into log files, and view those files to check the communication between the SMTP mail server and NetScanTools Pro.

#2. SMTP Email Relay Tester

It performs 15+ typical relay tests by interacting with an SMTP server. You can control which tests you want to run and view the test report as either HTML or text in your browser. This report also shows the communication between the targeted SMTP server and NetScanTools Pro.


SMTPPing is a simple and portable tool you can use to measure SMTP server delay, delay throughput, and variation.


My fellow developers, if you need a fast, zero-dependency platform for email testing based on the Go Programming Language, Mailpit is the ideal choice. Inspired by Mailhog (no longer maintained), Mailpit provides a modern web interface for testing and functions as an SMTP server.


This email tool operates from a single binary, requiring no installation. It includes SMTP functionality, a versatile web interface, HTML testing, link checking, real-time updates, and customizable settings.

It’s speedy, supports SMTP relaying, offers HTTPS and basic authentication options, and even provides Docker images for straightforward deployment.


MailHog gives you a good advantage since it’s based on the Go Programming Language. MailHog, a tool designed for developers, lets you set up your application to send emails through it.

You can then check these emails in a web interface or get them using JSON. If you want, you can also choose to send these emails to real email servers for delivery.


MailHog features include an ESMTP server, real-time updates, SMTP message release, Chaos Monkey, HTTP API, authentication, MIME support, storage options, and installation-free, providing enhanced email security and more.


LunaticSMTP, based on Java, functions as a faux SMTP server and features a JavaFX GUI for email app testing. This tool offers advanced capabilities to boost your SMTP testing efficiency. 


However, please note that to use LunaticSMTP, you must have the JavaFX module and Java 11 or higher installed, as they are essential for running and building the application.


MailDev simplifies testing emails with an easy-to-use web interface built on Node.js. Developers can also assess the responsive design of emails using a resizable viewport, making it both fantastic and practical.


Additionally, MailDev provides email management through an easily accessible RestAPI and offers notifications whenever a new email is received.


Mailocal is built on PHP, making it simple to set up a local SMTP server providing a convenient web interface for creating a stable testing environment. The installation process is straightforward, requiring just one command line: “composer create-project jfoucher/mailocal.” 


Additionally, you can specify a different database than the default SQL by providing the correct URL.


Sending emails to your readers, prospects, and clients are only the first step. It would be best if you always made an effort to find whether your emails reached their respective destinations successfully or not.

SMTP test and diagnostic tools help you maintain your SMTP server’s health by testing it and fixing potential risks. Thus, don’t take any chances of your next email ending up in the receiver’s spam box. Instead, use the above-mentioned SMTP tools to safeguard email security and increase deliverability.

  • Durga Prasad Acharya
    Durga Prasad Acharya is a Freelance Technical Writer who loves writing on emerging technologies, such as AI & ML, Cybersecurity, Web Hosting, SaaS, Cloud Computing, and more. Besides writing, he’s a web designer and is passionate about… read more
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