Open-source Email Verification – Top Tools for Marketers

Jun 6, 2024

Do you want your emails to reach the right people? Open-source email verification tools might be what you need.

open-source verification tool - cover photo

They help you check if an email address exists before you send a message, helping you save your sender reputation. 

Think of not having to worry about emails bouncing back or ending up in the wrong email inbox.

Our guide walks you through how these tools work and which ones are the best for keeping your contact list clean, for free (in most cases). Let’s get into it!

What is open-source email verification and how does it work?

Open source email verification is a handy process you can use to check if an email address exists. 

If you often need to verify email addresses, using an open-source email verification tool can save you a lot of hassle. You can check many emails quickly and know which ones are real, mistyped, or outdated.

How does it work? 🤔 You give the service an email address. It then sends a message to the mail server that is supposed to handle this email. If the server replies that the email address exists, you know it’s a real one. If the server says no, then it’s likely not a real email.

Open source email verification can help you in many ways, like keeping your contact list clean and up to date.

Pros and cons of using open-source email verification tools

It may sound super straightforward and only beneficial, but there are both pros and cons. 

Start with pros: 

Open source email verification service is free with most tools (but not all) 

One of the main perks of using open source email verification tools is that they are often free. 

You can use these tools to check if email addresses are real without spending a dime. That’s a big deal if you’re trying to keep costs down but still need a reliable email verifier. 

There are communities of developers that can help

Another plus of using open-source email verification tools is the support from communities of developers. 

When you have a problem or need to figure out how to do something like embedding the code into your website, you’re not alone. There are many people out there who also use these tools and know how they work.

Now, let’s talk about the cons. 

Could be more accurate 

Sometimes, when you use a free account with an open-source email validator, it might not catch all the errors in your lists. 

For example, it might say some email addresses are good when they are not.

If accuracy is crucial for your needs, you may consider some other option for catching invalid addresses. 

It requires knowledge of coding to set up and integrate into your tools or workflows

If you want to connect it to your tools or include it in your workflows, you need to know how to code. 

Not everyone is comfortable with coding, and if you are not, this could slow you down.

Top open source email verification tools 

If you would like to start bulk verification using open-source tools, and don’t know which one to use, here are some you might be interested in.

#1 Abstract API 

Abstract API - open source email verification

Abstract API is a free online tool designed for both bulk and real-time email verification. It’s not open source, you can’t access the code directly, but as users say, it’s easy to integrate into existing applications.


The service offers a free API key, allowing up to 100 requests, with 1 request/second. For heavier usage, paid plans start at $49 per month with 50,000 requests/month and 10 requests/second. There’s also an enterprise solution with custom pricing.


Setting up Abstract API is simple. Just sign up for a free account, receive an API key, and start using this key to make requests. The API checks various aspects of an email address like syntax, MX records, and the type of email (free, disposable, role-based), returning a JSON result with details on deliverability.


Abstract API performs several checks to ensure the accuracy of its email validation, including syntax validation, MX and DNS lookups, and real-time SMTP validation. It also identifies disposable and role-based email addresses.

Customer support

There are not many customer reviews regarding the quality of customer support. Users can reach out for help via email. However, unlike many other services, there’s no chat option available on the website. However, the service does offer extensive documentation to assist users.


Abstract API integrates smoothly with many tools and platforms your business might already use, such as cloud services like AWS and Azure, CRMs like Salesforce, and marketing platforms like Mailchimp and HubSpot. 

#2 Reacher

Reacher - online email validator

Reacher is a fully open-source email verification service. You can choose between using the open-source software for free or opting for the paid SaaS version if you need more robust features and support.


There’s a SaaS plan that lets you verify 10,000 emails per month for $69. If you need to host the service yourself, there is a commercial license available for $749 per month with unlimited email verifications. All plans come with a 30-day money-back guarantee.


To use Reacher, you can download it from GitHub and follow the installation instructions. 

You can set it up in three ways:

  • as a Docker instance on your mail server, 
  • as a CLI tool for command line verifications, 
  • or integrate it directly into Rust projects.

It fits well with different setups, whether you’re preventing spam sign-up forms or cleaning large email lists.


Reacher prides itself on the highest accuracy possible. It checks emails by connecting directly to the mail server to see if the email exists. 

It performs a comprehensive check that includes reachability, syntax validation, and many more parameters crucial for email deliverability.

Customer support

Reacher provides customer support through email and chat. You can also find plenty of useful information and guides on their GitHub page or their API documentation. 


The powerful API built into Reacher makes it easy to integrate the email validation API into your existing apps. 

Whether you need real-time or bulk email verification, Reacher’s API can handle it well. You can run your email verifier with their White Label solution, and keep your brand while using their technology.

#3 Truemail 

TrueMail - email checker

Truemail is a lightweight and configurable email verification API. It uses various methods to check if an email will actually reach the recipient’s inbox. You can adjust it to perform different levels of email validation according to your needs.


The tool is completely open-source, meaning it’s free to use. You can integrate and use it in your applications without any cost.


Setting up Truemail is straightforward if you’re familiar with Ruby*. You download the gem, configure it with your verifier email, and adjust settings like timeout durations and validation types. 

The setup lets you customize the email validation process to be as rigorous as you need, from simple regex checks to full SMTP verifications.

*Ruby is a popular, high-level programming language known for its simplicity and productivity. It’s often used for building web applications, especially with the Ruby on Rails framework, but it can also be used for data analysis, prototyping, and scripting among other tasks. 

When we talk about integrating Truemail into a Ruby application, it means adding the Truemail gem (a package or a library that contains a set of functionalities or resources that can be included and reused in Ruby applications) to a Ruby project to provide email validation functionality directly within that project.


Truemail performs detailed checks on email syntax, domain DNS records, and the real existence of an email account at the mailbox provider. 

It can adapt its validation techniques based on the specific requirements you set, such as using regex, MX records check, or direct SMTP interactions to ensure the email can reach the recipient’s inbox.

Customer support

Since Truemail is an open-source project, support mainly comes through community contributions on GitHub and the documentation provided on their website. 

While there may not be a direct customer service hotline, the extensive documentation and active community forums serve as substantial support resources.


As a Ruby gem, Truemail integrates naturally within Ruby applications. It does not come with built-in integrations for other services out of the box, but since it’s open-source, developers can customize it to work with other applications as needed. 

Truemail may be a good choice for developers looking to embed email verification capabilities directly into their Ruby projects.

#4 Verifalia

Verifalia - a tool for checking if an email exists

Verifalia is a tool that helps your emails reach their intended recipient by verifying email addresses. It offers a JavaScript package for integration into web applications and a public API that you can access online.


There’s a free option available that offers basic email verification capabilities. For more advanced features and higher usage limits, there are paid plans (starting at $9.90/month) that cater to small businesses up to enterprise-level organizations.


You can choose to integrate it directly into your web pages with a lightweight JavaScript widget, which doesn’t require much coding. 

Alternatively, for a more robust solution, you can import their full library into your project and interact with their API to check email addresses. There’s also the option to use their public API by accessing it through the website.


Verifalia guarantees high accuracy in verifying email addresses by checking several parameters, like syntax validation, domain validation, MX records, SMTP checks, catch-all domain verification, and more.

Customer support

There are various channels for customer support. They offer assistance for both their API and JavaScript packages, so you can get help when you need it to integrate their services or troubleshoot issues.


Whether you’re using JavaScript for a web project or connecting to their API from different programming environments, Verifalia fits easily into your existing systems. 

#5 Mailchecker

Mailchecker - for catching invalid emails

MailChecker is a useful tool to verify email addresses and improve email deliverability. It checks if email addresses are formatted correctly using Regex and identifies disposable emails by comparing them against a large database of known disposable domains.


MailChecker is completely free to use. You can download it from GitHub or NPM without any cost, making it accessible for anyone looking to clean up their email lists.


Setting up MailChecker is simple. After downloading the package, you can easily integrate it into applications written in various programming languages like Node, JavaScript, Python, Ruby, PHP, and more. 


MailChecker uses advanced Regex patterns provided by validator.js to ensure the email format is correct. 

It also checks each email against a comprehensive database of over 55,000 disposable email domains, which helps in accurately identifying non-permanent email addresses that could harm email deliverability.

Customer support

As a free tool, MailChecker’s support mainly comes from the community. Users can get help through GitHub issues where many users and the developer actively participate in discussions and provide solutions.


MailChecker can be integrated into just about any programming environment that supports its languages, including Node, JavaScript, Python, Ruby, PHP, Go, Clojure, Rust, and Elixir. 

Wide compatibility makes it an excellent choice for developers looking to incorporate email verification into diverse systems.

The better alternative to open source verification – Bouncer 

Bouncer for catching bad email addresses

Bouncer is an
email verification tool that helps you check email addresses quickly and accurately. It makes sure the emails you send are less likely to bounce and more likely to be delivered successfully.

Why is it a better choice?

Bouncer is a strong choice for email verification.

It provides lightning speed of verification and the best coverage – you can verify email addresses hosted by different email service providers (including deep catchall Google Workspace and Office365 verification) with a low amount of unknown results (0,3-3%).

Other winning features:


After signing up, you get your first 100 verifications for free. 

After that, you need to commit to one of the packages. The pricing is flexible, though. There are pay-as-you-go options and monthly plans (starting at $50/month for 10,000 verifications). You only pay for what you need, whether it’s a few thousand or a million verifications.

It reduces spam complaints and helps keep your email campaigns running smoothly.


Setting up Bouncer is easy. You sign up, get an API key, and start using it in your app or website, for example. 

Accuracy & speed

Bouncer is known for its high accuracy. It checks email addresses thoroughly to make sure they are valid and not just temporary or disposable. 

You can quickly check 200,000 emails per hour per customer.

Customer support

Bouncer has a reputation for great customer support. You can reach out via email or chat if you have any questions or need help with the setup.


Bouncer works well with other tools. You can integrate its email verification API into your applications to automatically check email addresses as they come in. 

👉🏻 Check out the list of tools Bouncer integrates with.

Bouncer features

Besides, reviews speak for themselves:

  • “stellar customer service”
  • “ I found the interface intuitive and user-friendly”
  • “I absolutely loved my experience with”
  • “ email verification service was remarkably accurate”

Bouncer's review


Bouncer's review



Now you know how open-source email verification tools can help keep your email list spotless and your messages on target. 

But if you want a tool that stands out for its ease of use, accuracy, and excellent customer support, look no further than Bouncer. 

Bouncer not only verifies emails quickly and accurately but also integrates smoothly into your existing systems to boost your email campaigns. 

So why wait? Start with Bouncer today and experience a cleaner email list and better delivery rates. Click here to sign up for Bouncer!

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