Last updated
February 28, 2024

Top 5 Best Open-Source Email Validation Tools

Elizabeth (Lizzie) Shipton

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Email verification is a critical step in successful email marketing. By verifying every address on your email list, you prevent fake and invalid emails from harming your sender reputation and lowering your deliverability score.

There are plenty of open-source tools and resources available to help you perform real-time and bulk email validation for your website or application. In this article, we’ll discuss these tools, and take an in-depth look at one free email verification API that can greatly improve your email deliverability.

Why Email Validation is Crucial for Your Business

Email marketing remains one of the most effective forms of online marketing. The ROI on successful email campaigns is as much as $36 to $42 return for every dollar spent. But that’s only true if your email list is robust and healthy.

Fake emails, disposable emails, free emails, spam traps, and other types of invalid email addresses can clog up your list and negatively impact the effectiveness of your email campaigns. These addresses do not belong to real users, leading to low engagement, and they often bounce, leading to high bounce rates.

They also take up valuable space on your list, meaning you pay your email provider to keep these useless and harmful addresses around.

Regular list cleaning via email validation allows you to detect and block these disposable email addresses and other types of invalid addresses so you can eliminate them from your list.

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Top Open Source Email Validation Tools

Let’s take a look at some of the best email verification tools available today. These are all open-source email verification tools, meaning the source code is freely available for anyone to look at or make changes to (as long as the changes are approved.)

The benefit of using open source software is that there is a whole community of developers and engineers constantly improving the code. You don’t have to wait for a large, slow organization to release updates. You also get the benefit of that community’s shared knowledge about the software, which can be useful when it comes to troubleshooting issues.

The downside of open source is that the tools are a little more complicated to integrate into your system and require some knowledge of coding.

Many open-source email verification services are free, but not all of them.

1. Reacher

Reacher is a fully open-source email verification service with over 4000 stars on GitHub and a most recent release of October 2023. It’s robust, actively maintained, and very popular. There is both an open-source and a paid SaaS version of the platform. Check out if you’d prefer to use the SaaS API.

To get started with Reacher, download the GitHub package and install it via the instructions in the docs. There are three ways to use it.

  • Create a Docker instance on your mail server. This allows you to send POST requests with emails for validation to your own hosted verification API.
  • Download the CLI and run one-off or bulk email verifications via your command line
  • Add the code as a library to your source code (this is only available for projects written in Rust.)

Reacher checks a whole list of parameters, including reachability, syntax validation, MX records, DNS records, SMTP server validation, role-based email detection, honeypot detection, spam trap detection, and whether the mailbox has been disabled.

2. Trumail

Trumail is a free, open-source email verification service written in Go. There are three ways to integrate the service into your app: a client library that you can download from GitHub, a publicly accessible API endpoint, and a public Docker Image.

The company offers a fully managed service to enterprise customers, but you can also use all of the tools for free on your own. It is worth noting that the last change to the repository was made 6 years ago - this means that no one is actively working on the code anymore, but it also means the code is stable and unlikely to change or break.

Getting started with the service is easy - just download the GitHub repo using the link provided or your command line. The documentation is included in the repo. You can also visit to get an API key for the public endpoint if that’s all you plan to use.

3. Verifalia

Verifalia is similar to Trumail in that it provides access via either a public API endpoint or a  JavaScript package you can download via NPM.

There are two versions of the JavaScript package: a full library you can import into your source code that exposes email verification methods to interact with their API or a lightweight JavaScript widget that you can add to a single web page without writing any code.

There is also a publicly accessible API at that has several pricing tiers ranging from free to enterprise-level needs.

The last change to the Verifalia source code was made two months ago, which indicates the repo is active and currently maintained. There are over 2000 downloads of the code every week, indicating that it is a popular service with a robust developer community behind it.

4. MailChecker

MailChecker is a cross-language email verification tool that allows you to verify email addresses using Regex to check that they are properly formatted. It also helps you discover free and disposable email addresses by checking emails against a database of over 55,000 known disposable domains.

You can download MailChecker via Github. It supports Node, Javascript, Python, Ruby, PHP, Go, Clojure, Rust, and Elixir. Under the hood, it uses validator.js to check email formatting, and its own email validation API to check for disposable domains.

Here’s a simplified example of how to implement MailChecker in your Node app once you’ve downloaded the package.

var MailChecker = require('mailchecker');



The most recent release to this repo was 3 months ago, so it’s actively maintained.

5. Email Verifier

Email Verifier is another popular Github repo with 1000 stars. It was most recently updated in January 2024, so it is active, however, it is not as well-used as some of the other options on this list.

The package is written in Go and integrates with Go applications. The easiest way to use it is to install it in your app and use the exposed Verify method. The method accepts a string and checks to see if the string contains a valid email address.

The package also does SMTP lookup, checks MX records and DNS, and does a reachability test.

Abstract API

Abstract API is a free online email verification API that does both bulk and real-time email verification. It is not open source (the code is not readily available to read or download online) but it is very easy to integrate into your existing app.

To use the API, simply sign up for a free account and get an API key. You can then use this key to make requests against the public endpoint. The service does syntax validation, looks up MX records and DNS, checks for free, disposable, and role-based emails, and returns a JSON result containing an easy-to-parse evaluation of the email’s deliverability.

There is a free-for-life tier that allows up to 1000 requests per month and paid tiers that range from $9/month for basic usage up to $499/month for enterprise customers.

Github StarsMost RecentReleaseHas Paid PlanLanguages SupportedValidates MX/DNS/SMTP


4.1KFeb 2024YesAPI/Docker - all,library - RustYes


1K2018NoAPI/Docker - all,Library - GoYes


9Jan 2024YesAPI - all,Library - JavascriptYes


1.6KNov 2023NoAPI - all, library - Node, PHP, Go, Ruby, Rust, ClojureNo


1KJan 2024NoGoYes



Why You Should Consider Abstract API

When it comes to email address validation for email marketing campaigns, you need a service that is fast, reasonably priced, and reliable.

Abstract API provides a secure, easily accessible email validation endpoint. There are no libraries or packages to download - simply make a network request to the endpoint with the emails that you need to check. The service is completely language-agnostic and requires no install or setup.

You can start for free and quickly build a test app using the free-for-life tier. Once you’re ready to deploy to production scale, just upgrade your account to the tier that supports the number of requests your app will need to make.

The Technicalities of Email Validation

There are several factors to consider when doing robust email validation. You need to check not only that the email exists and is properly formatted, but also need to verify that it is valid and deliverable. Validity and deliverability depend on many things:

  • MX records
  • DNS records
  • SMTP setup
  • Free/disposable addresses
  • Spam traps
  • Catch-all emails

Best Practices

When implementing email validation, it’s important to make sure you’re adhering to all applicable privacy laws and doing your due diligence to protect your users’ personal information.

  • Always check that the service you use complies with GDPR, CDPA, and all other privacy legislation
  • Bulk clean your email list to remove invalid emails at least once every 6 months
  • Maintain your list by implementing real-time checks on any web pages that contain user sign-up forms.
  • Provide an unsubscribe link that is easily visible at the bottom of every email you send
  • Don’t spam users
  • Don’t sell user information to third parties

Conclusion: Integrating Open Source Email Validation into Your Workflow

Open-source software is a powerful way for both enterprise and small businesses to leverage email validation. While it does require some technical skill to get up and running, the flexibility provided by writing your code using open-source packages means you will have total control over your software.

If open-source tools are too complicated for your team, consider a publicly available API instead. Many open-source services provide an API endpoint in addition to their downloadable packages. AbstractAPI is one such service, and it’s a great way to get started with email verification.

Get started by creating a free account with Abstract API today.


What free tool can you use to verify if an email address is valid?

There are many free email checker tools out there that can help you determine whether or not an address is valid. They include AbstractAPI’s Free Email Validation API, Trumail, Reacher, Verifalia, Email Hunter, and the free tiers of NeverBounce and ZeroBounce.

What is open source?

Open source software is software with source code that is made freely accessible online, for anyone to view and modify. The benefit of open source is that many people can update and make changes to the code, meaning that bug fixes and new features happen quickly, and there is a wealth of community knowledge available to help people learn to use the software and troubleshoot issues.

How do I validate email using an API?

To validate an email address using an API, sign up for an account with the API and get an API key. You’ll include this key in your code when you send network requests to the endpoint. You can send requests via the command line or by programmatically coding the request into your app or website.

How can using an email validation API reduce the number of spam complaints my email campaigns receive?

Email validation APIs can significantly reduce spam complaints by ensuring that emails are sent only to valid and active email addresses. By filtering out invalid, disposable, or risky email addresses that could mark your emails as spam, these APIs help maintain your sender reputation and ensure your emails reach the inbox of engaged recipients.

What impact does email validation have on the ROI of email marketing campaigns?

Implementing email validation can have a positive impact on the ROI of email marketing campaigns. By cleaning your email list of invalid and non-responsive addresses, you improve deliverability and engagement rates. This leads to higher open and click-through rates, driving better campaign performance and ultimately enhancing the ROI of your email marketing efforts.

What are the differences between real-time and bulk email validation, and when should each be used?

Real-time email validation occurs at the point of email capture, such as during sign-up forms or account registrations, instantly verifying the validity of an email address. It's ideal for preventing the accumulation of invalid emails from the start. Bulk email validation, on the other hand, is the process of cleaning an existing email list by verifying the validity of all email addresses in bulk. It's best used periodically to maintain the health of your email list over time.

Elizabeth (Lizzie) Shipton
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