10 Best SMTP Test Tools

Email troubleshooting is a must for all organizations that greatly rely on email communications regardless of purpose. That probably translates to all companies worldwide today given these statistics:

• Close to 4.5 billion people worldwide use email as of 2025.
• 88% of users check emails as many as 3–5 times a day.
• Automated emails generate 320% more revenue than nonautomated messages.
• Every US$1 spent on email marketing returns an average of US$36.
• 59% of consumers say marketing emails influence their purchase decisions.

But, organizations should also know that given the technology’s ubiquity, many threat actors leverage emails in their malicious campaigns as evidenced by these numbers:

• More than 90% of cyber attacks begin with phishing.
• 75% of cyber attacks start with a deceptive email.

All these facts can be considered proof of the importance companies should accord to Simple Mail Transfer Protocol (SMTP) testing. Find out what SMTP testing is and more in this post. And if you are currently in the market for one, maybe we can help you make the right choice.

What Is SMTP Testing?

SMTP testing helps users check if their outgoing emails abide by SMTP rules. As such, the process examines every aspect of email sending and receiving, including IP address setup, port use, security protocol usage, and email routing to ensure messages are received and sent safely.

The test is crucial when setting up new mail servers, periodically testing existing mail servers, troubleshooting email delivery issues, validating configuration changes to mail servers, and monitoring email performance to identify bottlenecks.

SMTP testing essentially mimics the email-sending process to identify flaws manifested in error messages, logs, and reports. It complements email verification that automatically determines if recipient email addresses are reachable and flags typos or other reasons why message-sending may fail.

What Are the Reasons for SMTP Testing?

SMTP testing acts as an organization’s first line of defense in email deliverability and security. We listed a few key reasons why routine testing is important.

Make Sure Emails Are Received and Delivered

The test’s primary goal is to check if your mail server can deliver and receive emails without any trouble. It can help identify problems like malformed Domain Name System (DNS) records, firewall limits, and hardware issues.

Find Security Vulnerabilities

The test helps security teams uncover email system flaws that threat actors can exploit. Finding and fixing security vulnerabilities protects not only the company’s data but also its customers, suppliers, and stakeholders.

Avoid Spam Traps

All email service providers use advanced systems that prevent spam from reaching users. Emails may end up in spam folders if they get flagged for suspicious content or IP authentication and Sender Policy Framework (SPF) record issues. The test helps check for these problems.

Maintain a Reputable Server

Email servers that have been tagged as spam senders or security issues can earn reputational damage—their IP addresses or domains may get blacklisted. That could ruin your entire business’s reputation, which would make email sending difficult. Proactive SMTP testing can help you keep your reputation intact.

Identify Performance Issues

Regular SMTP load testing, just one part of the process, shows how much traffic email servers handle. That way, organizations can upgrade them to match traffic growth. Performance problems can also affect service operations.

Minimize Business Disruption

The test helps companies avoid email outages that can delay operations and communication.

What Are the Steps in SMTP Testing?

While the SMTP testing steps will vary based on the tool an organization uses, the general process below illustrates the broad phases followed.

1. Set up test configurations.

The first step requires choosing the infrastructure components (e.g., email addresses, mailboxes, and domain names) and servers for testing. Create a testing area separate from your primary production system.

2. Configure test prerequisites.

Next, set up all the necessary user permissions and network settings so you can test systems without disrupting your operations.

3. Establish SMTP connections.

Do a basic network check by starting an SMTP session with your mail servers to test their initial availability. Do not forget to ensure that connections are encrypted.

4. Verify SMTP functionality.

Test server operations by running the following SMTP commands to validate your configuration settings:

• HELO/EHLO
• MAIL FROM
• RCPT TO
• DATA

5. Test email functionality.

Next, send test emails with various content and embedded media, attachments, and malware to see how well your security filters work while testing email delivery and movement.

6. Analyze delivery reports.

Study the test reports that show delivery results, spam risk scores, and connection details. Look at performance metrics as well to see if anything requires improvement.

7. Retest after addressing issues.

After addressing problems with your setup, rules, and equipment, test again to confirm they have been resolved.

10 Best SMTP Test Tools

After learning more about SMTP testing, you may wish to take a look at possible options for your organization’s use.

1. CheckTLS

CheckTLS tests mail servers’ ability to send and receive encrypted emails. It simulates email sending between two domains to see if they support Transport Layer Security (TLS) from end to end.

The product also offers full email delivery diagnostics, header analysis, and DNS record checks. It is ideal for organizations in regulated industries where encryption is nonnegotiable.

You can choose from two subscription plans—Corporate and Professional.

2. Mailgun SMTP Logs and Test Mode

Mailgun users can use its SMTP logs to look at full delivery paths, retry attempts, and bounce responses. These logs give a detailed view of SMTP transactions for troubleshooting.

The tool also has a test mode where users can simulate full send cycles without actually sending emails. It is ideal for application programming interface (API)-driven applications.

Users can try it free of charge or choose from three paid plans—Basic at US$15 a month, Foundation at US$35 a month, and Scale at US$90 a month.

3. Mailtrap Email API/SMTP and Email Sandbox

Mailtrap’s Email API/SMTP and Email Sandbox test systems by creating fake SMTP environments that enable testing without actually sending messages to real users. It captures entire SMTP transactions, shows headers, and spam scores. It also allows users to debug email code safely.

It is ideal for developers who need to validate email logic before going live. It also lets them run authentication and TLS checks during development.

Email API/SMTP can be used free of charge. It also has three subscription options—Basic at US$15 a month, Business at US$85 a month, and Enterprise at US$750 a month.

Email Sandbox, meanwhile, also has a free option and four paid plan choices—Basic at US$17 a month, Team at US$42 a month, Business at US$123 a month, and Enterprise at US$498 a month.

4. MXToolbox

MXToolbox is a free SMTP diagnostics tool that lets you check open relay status, test TLS encryption, and inspect headers. It also determines your blacklist status and offers DNS lookups for SPF, DomainKeys Identified Mail (DKIM), and Domain-Based Message Authentication, Reporting, and Conformance (DMARC).

To use it, just enter your domain name or IP address. It will provide you with a detailed breakdown showing how your mail server responds to SMTP commands. It is fast and works for both one-off tests and ongoing monitoring.

5. Paubox SMTP API

Paubox SMTP API provides encrypted email services and checks if outbound emails use secure TLS channels.

It is well-suited for healthcare organizations that deal with sensitive data as it validates headers and confirms Health Insurance Portability and Accountability Act (HIPAA)-safe delivery paths.

Interested parties can subscribe to any of three plans—Standard at US$29 a month, Plus at US$59 a month, and Premium at US$69 a month.

6. Pingability SMTP Tester

Pingability’s SMTP Tester is a free tool that focuses on uptime. It runs regular SMTP checks across global servers and notifies users if their servers are down, slow, or misconfigured.

It is ideal for ongoing monitoring and alerts DevOps teams even before users report issues.

7. Postmark SMTP Service

Postmark’s SMTP Service focuses on email delivery performance and reliability. It shows how fast emails get sent and what may be slowing them down. It offers SMTP speed and delay tracking, authentication response analysis, inbox delivery timeline, and error tracing for SMTP retries.

The tool works best for product teams and software-as-a-service (SaaS) companies that send critical alerts, receipts, and transactional messages.

It has a free trial. Users who want to continue using the service can opt for any of three subscriptions—Basic at US$15 a month, Pro at US$16.50 a month, and Platform at US$18 a month.

7. Qualys SSL Labs SSL Server Test

While not built primarily for SMTP testing, SSL Server Test can scan mail servers’ Secure Sockets Layer (SSL)/TLS setups. It checks for weak ciphers, expired certificates, and outdated protocols.

Organizations can use it free of charge to ensure their encrypted emails cannot get exposed to downgrade attacks due to poor security practices.

8. SocketLabs SMTP Diagnostics, Test, & Monitoring Tool

SocketLabs’s SMTP Diagnostics, Test, & Monitoring Tool checks SMTP credentials, host and port configurations, and encryption. It gives detailed logs of send attempts, including where and why they failed.

The product also provides real-time feedback on blacklist status and spam triggers. It is useful for managing email marketing at scale and providing deep diagnostics.

Users can avail of it for free or subscribe to one of two plans—Pro 100k at US$79.95 or Enterprise at a custom price.

10. Wormly SMTP Test

Wormly’s SMTP Test is easy to use. All users need to do is type their server details. It checks command responses, TLS support, and authentication enforcement.

It is useful for basic checks and gives users clear response codes and errors in one go.

The product is available for free or via four subscription plans—Startip at US$44 a month, Agency at US$107 a month, DevOps at US$221 a month, and Enterprise at US$562 a month.

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These days, sending emails without SMTP testing is like driving without checking your car for fuel. Keep in mind that successful tests ensure correct SMTP configurations and your email system works as it should.