Blog Post: tech | Sep 1, 2022

The Halon MTA vs. open source MTAs

As demand for secure, safe and timely emails increase, companies need to future-proof themselves in order to keep up with the ever-changing market. A Mail Transfer Agent (MTA) that is nimble, scalable and secure will revolutionize your tech stack and ensure you stay ahead of the competition.

At Halon, we understand standards change and so do needs. That’s why Halon is the developers’ choice MTA for secure and growth-proof email infrastructures — built to be scaled, changed and challenged at pace. Halon is a full-stack toolbox that offers the perfect blend of ready-made components and an expert team to support you every step of the way.

Compared to open source solutions such as Postfix or Exim, the Halon MTA offers an unrivaled extensive list of features and benefits that can help you:

• Reduce complexity enabling resources to spend more time on revenue-generating tasks and ensuring a lower Total Cost of Ownership (TCO)
• Simplify operations with the possibility of a more granular approach, leading to avoidance of issues such as blocklisting
• Optimize performance and reduce code and hardware by 70% with modern configuration tools
• Deliver timely and up-to-date features and security protocols, leading to a competitive service offering and happier customers.

Furthermore, some of the main components that set the Halon MTA apart from the rest are:

1. Better queue and policy management
2. A modernized approach to configuration
3. Features aimed toward large production environments and significant performance improvements
4. Scalability and container optimization
5. Extensive library of ready-made features and integrations

Let’s dive into these a bit more.

1. Queue and policy
Ensures maximum deliverability even under a heavy load and with complex workflows, while at the same time being straightforward and easy to modify.

In contrast to alternative open source products, the Halon MTA offers features that enable you to precisely tailor your deliveries to your customers. With minimal effort, a configuration that limits the concurrency and rates for specific destinations can be implemented, based on any available data such as source IP. The Halon MTA supports MX rollup which makes it very easy to write policies for large mailbox providers that serve a large number of domains, like Google and Microsoft. Functionality that temporarily suspends sending IPs when encountering deliverability problems can quickly be implemented as well.

2. Configuration
Extremely flexible and powerful configuration format enables rapid development of new features and very easy to overview policy-as-code.

Instead of using configuration files with static values, and then hooking into external scripts running on the server, the Halon MTA uses a domain-specific scripting language that packages all of this for you. With this approach to configuration, you can specifically tailor every part of the SMTP transaction to do exactly what you want with very little effort. Features like doing LDAP lookups, IP reputation checks, spam filtering and anti-virus can easily be configured within a single configuration, packaged and easily deployed.

3. Production features and performance
Minimize downtime and mishaps with tools for deployment, testing and debugging while at the same time being very fast with minimal overhead.

The Halon MTA is designed to be run in very large environments. To achieve this we’ve implemented a few key differences in comparison to open source alternatives. Firstly the queue management runs in an asynchronous manner, meaning that the MTA can handle tens of thousands of concurrent connections without performance penalties. The queue management is also highly optimized with only critical metadata being kept in memory which means that it’s just as fast with a thousand messages in the queue as with several million. Data resilience can also be tuned on a per message basis, allowing you to fine-tune things like fsync and pass through delivery, lowering the hit on disks. Secondly, features like blue-green deployment allow you to gradually move user traffic over to a new configuration in a controlled manner. Halon supplies all the necessary tools to work with the MTA in a production environment like plugins for Visual Studio Code and APIs to integrate with the production environment.

4. Container ready
Support stateless configuration, and single binary operation for easy deployment and autoscaling. Thoroughly tested in containerized environments.

The Halon MTA is optimized to run in a microservice environment and has been designed to run as a single binary application, perfect for containerised environments. While also supporting features like integrations to all major logging solutions and supporting a totally stateless setup with pass-through delivery for inbound mail flow. Extra components like spam filtering, anti-virus and cluster-wide rate daemons can be run in separate containers and easily be auto-scaled.

5. Modules, integrations and threat protection
Halon comes as a package with threat protection or with turnkey integrations to incumbent software used, and together with a modularized feature library, customers have the best of both worlds in simplicity and flexibility.

Halon has an extensive history of collaboration within the threat protection community and is a member of the Messaging, Malware and Mobile Anti-Abuse Working Group (M3AAWG) and partner of the Senders Certified Alliance (CSA). We provide ready-made integrations for all major content filter providers in the field, provided as ready-made components, for everything from integrations to threat protection providers, to deliverability feeds and dashboards. We partner with Cyren (since 2006) and Sophos and can provide those integrations packed and ready to go. Most of our integrations are provided as officially supported open source modules to enable the flexibility to be tailored to each specific need. Plus, as a customer, you will have access to our open source modules on Github which serves as a library of ready-made features that can be added to enhance your MTA.

Ready to find out more about the Halon MTA? Contact us at and one of our friendly representatives will be in touch with you.