As 2025 draws to a close, we’re wrapping up our third year working on KumoMTA (our first commit was in March of 2023). Our first year centered on building the MVP, and our second on our initial production deployments; this third year has been defined by growth.

A Year of Exponential Growth

KumoMTA and its community have grown dramatically by every measure:

• We doubled the number of community members in our Discord.
• We doubled the number of releases compared to last year (changelog).
• We doubled the number of sponsors supporting KumoMTA.
• We doubled the number of contributors to the KumoMTA repo, most of whom are community volunteers.
• We tripled the size of the paid KumoMTA team, which now spans the globe with team members on three continents!

We also enjoyed hearing of the growth of our sponsors and users, with many leveraging KumoMTA for the first time during Black Friday/Cyber Monday without issue, a time which typically doubles daily sending volume. We had zero support requests over the BFCM window, a testament to how well prepared our sponsors were leading up to the critical sending weekend.

Expanding Our Horizons

From its inception, KumoMTA has had the attention of not only large-scale enterprise email senders, but there has also been significant interest from large-scale email security vendors and mailbox providers.

We built KumoMTA on a very flexible architecture with a Lua policy layer to enable almost limitless use cases for our users, and we have had several users implement receiving use cases even before we updated KumoMTA to support them natively.

We maintained a roadmap of features and functionalities for receiving use cases, but decided to maintain focus on enterprise senders until we had a sponsor who wanted to support the development of KumoMTA’s receiving capabilities.

We’re pleased to say that we were approached by a sponsor who was looking to replace their aging inbound MTA architecture and who was eager to sponsor KumoMTA’s receiving roadmap. Those features were rolled out continuously in our dev branch, and the first stable release with receiving features was made in May 2025 (changelog)! 

At this point KumoMTA is built for both senders and receivers, with the capabilities and flexibility needed for processing millions of messages per hour per server in both inbound and outbound environments. In addition, senders can use the receiving capabilities of KumoMTA to validate and test outbound message streams for compliance before those messages leave the sender’s environment, adding a final line of defense against abuse originating from their network due to malicious users and compromised accounts.

A Global Community

KumoMTA is more than just an MTA, it’s a growing global community of MailOps professionals and contributors. Not only did we enjoy watching the Discord community double in size, we loved getting to meet even more community members in 2025 through community dinners and events in Vancouver, Amsterdam, Charlotte, London, and Portugal.

We now have community members from every continent (except Antarctica) and have a growing group of contributors that are helping to increase the functionality of KumoMTA.

One thing to note: we do not require our contributors to sign any contributor agreements when adding code to KumoMTA (though we do work with them to ensure that the contributions are secure and of high quality). This strengthens our commitment to keeping KumoMTA open source by spreading ownership of the KumoMTA codebase to a wider pool of contributors, keeping both ourselves and any future successors from owning all the code and opting to take it closed-source.

Giving Back

One of our favorite parts of the success of KumoMTA is our opportunity to give back in various ways. We have been able to sponsor upstream projects as well as provide code contributions, and have been able to sponsor projects related to our MailOps community, including being a Diamond sponsor for the 2025 Mautic conference.

We love growing not only our KumoMTA community but the larger email community, which is why we’ve been happy to support Email Expert and the Deliverability Summit over the years and look forward to continuing to do so going forward.

The Best is Yet to Come

Looking forward, we can already tell that 2026 is going to be a busy year. The number of enterprise senders testing KumoMTA is truly mind-blowing, as is the estimated volume of production mail expected to come online in the coming year. 2026 is the year we go from measuring annual KumoMTA usage in terms of billions of messages to instead measuring it in terms of trillions of messages.

2026 is going to be about more than just usage growth, we anticipate seeing both our community as well as our team double again in 2026, with a focus in the coming year on quality of life improvements for our users. In 2025 we extended KumoMTA to make anything possible, in 2026 we’re going to make everything even easier to achieve with more pre-built use-cases, more ways to manage KumoMTA, and even better automations, all without the black-box risks and vendor dependency of AI, instead ensuring that our users are in control of their email infrastructure every step of the way.

We plan to meet even more of our community through more events, both online and in-person, and support and sponsor our upstream contributors even further; we know that KumoMTA isn’t just the product of a couple of dozen direct contributors, but is built on the strength of hundreds of developers in the Rust ecosystem, and our success is theirs as well.

It’s All Thanks To You

If you’re reading this, you have our thanks. At the end of the day a project like KumoMTA is only as strong as its community, and we’ve seen a wonderful community gather around KumoMTA.

We’ve seen so much support from the KumoMTA community including financial support from our sponsors, peer support in our Discord, community contributions in our Github repository, and community generated content online in a variety of ways. 

Even just spreading the word about KumoMTA has helped us grow and succeed, we appreciate how much word of mouth has been a factor in the success of KumoMTA.

Let’s see what we can do together in 2026.

Thanks,

Mike, Tom, and Wez

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KumoMTA is the first open-source MTA designed from the ground up for the world's largest commercial senders. We are fueled by Professional Services and Sponsorship revenue.

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