What Is SMTP Testing? Benefits, Tools & How to Do

ByHimadri Sharma


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Imagine you're the manager of a bustling postal service, responsible for the successful and secure transmission of letters and packages to their destinations. Your post office system relies on a network of mail carriers, sorting facilities, and delivery routes to get the job done efficiently.

Now, think of SMTP testing as conducting a comprehensive inspection of your entire postal system. It's like sending a team of inspectors to scrutinize every aspect of your operation. As a manager, you'd want everything to be flawless and work perfectly. To do this, you'd check every part of the system and make sure everything is working perfectly.

This inspection is the same as SMTP testing in case of delivery of emails. This is why, you would test your entire system to be flawless for email delivery. SMTP testing ensures your server settings are optimized, acting as your quality control for seamless email transmission.

In this guide, we'll delve into the intricacies of SMTP testing, unraveling its importance, the various tests involved, and how to ace your SMTP game like a pro.

Table of contents

What is SMTP testing?

SMTP testing is a process that verifies the functionality of your Simple Mail Transfer Protocol (SMTP) server settings. During the process, it checks if your email server is set up correctly and can send and receive emails securely and reliably.

Why do you need to do an SMTP test?

Imagine mailing a letter without double-checking the address, only to be lost in transit. SMTP testing prevents the online version of such mishaps, which means that it ensures your emails reach their destination and dodge the dreaded spam folder. From pinpointing configuration blunders to thwarting spam attacks, SMTP testing helps solve all issues with your email.

Here are some of the reasons why running an SMTP test is essential.

Ensure deliverability

SMTP tests verify that your email server is properly configured and capable of sending and receiving emails. This ensures that your emails reach their intended recipients' inboxes rather than being flagged as spam or bouncing back.

Just like ensuring a letter has the correct address and the right stamps required so it doesn't get lost in the mail.

Detect configuration issues

By conducting SMTP tests, you can identify any configuration errors or issues with your email server setup. This includes problems such as incorrect DNS records, misconfigured SMTP settings, or blocked ports, all of which can hinder email delivery.

Prevent spamming

SMTP tests help prevent your email server from being exploited by spammers. By ensuring that only authorized users can send emails through your server and implementing proper authentication mechanisms, you can reduce the risk of your server being blacklisted or used for malicious purposes.

Maintain a good reputation

By proactively monitoring and resolving any issues that may affect email deliverability, you can ensure that ISPs trust your emails and that your domain and email server has a good reputation, which prevents them from being marked as spam.

Proactive troubleshooting

It helps catch the specific problems early on, saving time and frustration compared to undelivered emails later and frustrated customers down the line. Just like identifying and fixing a minor software bug in your website before it causes the entire site to crash. Similar to maintaining your phone’s software updates to avoid dropped calls and glitches.

Enhances security

Confirms that your email server is secure and protected against unauthorized access and email spoofing. Just like having a security system at home to prevent intruders from breaking in.

Improve customer communication

Reliable email delivery is crucial for maintaining effective communication with your customers. SMTP tests help ensure that your emails are consistently delivered on time, allowing you to provide timely updates, support, and marketing messages to your audience.

Different types of SMTP tests

SMTP tests come in various forms, each serving a unique purpose:

  1. Connection testing: Verifying that the email server can connect with other mail servers over the SMTP protocol. This ensures that the server is reachable and can send and receive emails.

  2. Authentication testing: Checking the authentication mechanisms implemented on the email server to ensure that only authorized users can send emails. This includes testing SMTP authentication methods such as SMTP-AUTH, SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance).

  3. DNS configuration testing: Verifying that the DNS (Domain Name System) records associated with the email domain are correctly configured. This includes checking MX (Mail Exchange) records to ensure emails are routed to the correct mail server and verifying SPF, DKIM, and DMARC records for proper authentication and validation.

  4. Port and protocol testing: Ensuring that the email server is listening on the correct ports (typically port 25 for SMTP) and supporting the necessary protocols (e.g., STARTTLS for secure communication). This helps prevent issues related to blocked ports or unsupported protocols.

  5. Relay testing: Checking whether the email server is configured to allow unauthorized relaying, which can be exploited by spammers to send spam emails through the server. Relay testing ensures that the server only relays emails from authenticated and authorized users.

  6. Delivery testing: Sending test emails to verify that the email server can successfully deliver emails to recipients' inboxes without being flagged as spam or bouncing back. This includes testing for factors such as message formatting, attachment handling, and spam filtering.

Step-by-step guide to performing SMTP testing

For conducting successful SMTP tests configuring your SMTP server is a must. It involves setting up the server address, specifying the appropriate ports, enabling security protocols if required, and configuring authentication settings. Here are the steps to configure your SMTP server for testing:

Step 1: Obtain the SMTP server configuration details from your email provider or SMTP delivery service. This typically includes the server address, port number, security settings, and authentication requirements.

Step 2: Open your email client or SMTP testing tool and navigate to the SMTP server settings.

Step 3: Enter the server address provided by your email provider or SMTP delivery service.

Step 4: Specify the appropriate port number for SMTP communication.

Step 5: Enable the required security protocols, such as TLS or SSL, depending on the server's requirements.

Step 6: Specify the sender's and recipient's email addresses to simulate the sending of a test email.

Step 7: Check the option for a secure connection if required by the SMTP server.

Step 8: If authentication is required, enter the username and password provided by your email provider or SMTP delivery service.

Step 9: Hit the "Test SMTP" button to initiate the test.

Step 10: Analyze the test results to identify any issues or errors. This includes checking for successful connection establishment, email delivery, and any error messages received.

By configuring your SMTP server correctly, you ensure that the testing process is accurate and reflective of the actual email delivery settings.

SMTP testing using commands

In addition to basic SMTP testing, there are advanced techniques that can further enhance the effectiveness of your testing process. These techniques involve testing using the commands. There are 17 different SMTP testing commands given below:

Command name Command form Command description
HELO/EHLO HELO<SP><domain><CRLF> OR EHLO<SP><domain><CRLF> When an email client wants to start a conversation with the email server, it says “HELO” or “EHLO” followed by its domain name.
MAIL FROM MAIL<SP>FROM : <reverse-path><CRLF> The email client introduces the sender of the email using the "MAIL FROM" command.
RCPT TO RCPT<SP>TO : <forward-path><CRLF> The client specifies the recipient using "RCPT TO."
DATA DATA<CRLF> The client uses the "DATA" command to indicate that the message body is about to be sent.
RSET RSET<CRLF> The "RSET" command allows you to reset the conversation without disconnecting.
VRFY VRFY<SP><string><CRLF> The "VRFY" command asks the server to verify if a particular email address exists.
EXPN EXPN<SP><string><CRLF> The "EXPN" command asks the server to expand a mailing list and provide all the email addresses included in it.
HELP HELP<SP><string><CRLF> The "HELP" command asks the server for assistance and a list of available commands.
NOOP NOOP<CRLF> The "NOOP" command does nothing but elicit a response from the server to keep the connection alive.
QUIT QUIT<CRLF> The "QUIT" command gracefully closes the conversation.
TURN TURN<CRLF> The "TURN" command allows the client and server to switch roles.
AUTH AUTH<SP><mechanism><CRLF> The "AUTH" command is used for the client to prove its identity.
STARTTLS STARTTLS<CRLF> The "STARTTLS" command initiates a secure encrypted connection.
ATRN ATRN<SP><domain><CRLF> The "ATRN" command is used for on-demand mail relay.
SOML SOML<SP>FROM : <reverse-path><CRLF> The "SOML" (Send Or Mail) command sends the message to the recipient if they are currently connected. If they are not, it sends the message to their mailbox.
SEND SEND<SP>FROM : <reverse-path><CRLF> The "SEND" command sends the email to the recipient only if they are currently connected. If they are not, the message is not sent and no attempt is made to store it.
SAML SAML<SP>FROM : <reverse-path><CRLF> The "SAML" (Send And Mail) command sends the message to the recipient if they are currently connected. If they are not, it also stores the message in their mailbox for later retrieval.

Mastering these SMTP commands empowers you to navigate the digital postal realm with finesse, ensuring efficient communication and seamless delivery of messages.

5 automated SMTP testing tools and software

Automated SMTP testing tools and software offer a more convenient and efficient way to conduct SMTP tests. These tools automate the process of sending test emails, checking various parameters, and analyzing the results. Here are some popular automated SMTP testing tools and software:

  1. SMTP. com: This tool provides comprehensive SMTP testing functionalities, including email delivery testing, connection monitoring, and performance analysis.

  2. WP Mail SMTP: This WordPress plugin allows you to test your SMTP server directly from your WordPress dashboard. It offers a user-friendly interface and provides detailed test results.

  3. Mailtrap: Offers secure email testing with features like spam testing and email validation, along with detailed reporting and analytics. It provides flexible pricing, including a free plan for basic testing needs.

  4. SocketLabs: Delivers robust SMTP testing, including connection and performance tests, with real-time alerts and comprehensive analytics. It features a free trial and varied pricing plans to suit different needs.

  5. SMTP Diag tool: Simplifies SMTP server testing and delivery issue diagnosis with its intuitive interface and real-time reporting. It's a free tool, ideal for basic SMTP testing requirements.

By utilizing automated SMTP testing tools and software, you can streamline the testing process, save time, and ensure accurate results.


So, as you navigate the vast expanse of the digital postal realm, armed with insights into SMTP testing intricacies and with automated tools, rest assured following the given practices and testing steps your messages will traverse the digital highways with finesse. By embracing the ethos of proactive testing, you not only safeguard the integrity of your communication but also nurture enduring relationships with your audience.


SMTP testing verifies the functionality and performance of an SMTP server.

It ensures reliable email delivery and identifies potential issues in the mail server configuration.

Use tools like Telnet, OpenSSL, or dedicated SMTP testing software.

It involves connecting to the SMTP server via Telnet to send email commands manually.

Open Telnet, connect to your SMTP server on port 25, and enter SMTP commands.

Possible reasons include misconfiguration, network issues, or spam filters.

You can automate smtp testing using scripts or software like Postfix, Sendmail, or third-party SMTP testers.

Slow response times, frequent errors, or failed email deliveries are a few reasons for the failure of the SMTP server.

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