KumoMTA Case Study – Puresend
Puresend successfully navigates tumult and consolidation in the email server industry with help from KumoMTA
A long-established boutique email services provider (ESP) based in New York, Puresend has built a strong reputation as a self-service email shop that combines powerful sending capabilities with close attention to customer needs. Companies rely on Puresend for outstanding campaign performance, deliverability and engagement results, backed by deep expertise earned over 20+ years in the email industry.
For many years, the company had relied on the Momentum message transfer agent (MTA) as the delivery engine for its flagship Purecast email sending and reporting platform. Through several waves of consolidation in the MTA space, the Momentum product went through multiple changes to the point where the Pursend team decided they needed to make a change. Puresend initially migrated to PowerMTA, but found it inadequate as well. In 2024, based on market research and with deep connections in the email space, the team decided that working with KumoMTA was the best path forward.
The Solution - With a Little Help From Some Old Friends.
Founded by engineers who had a hand in the development, deployment and support of Momentum many years ago, KumoMTA represents a new model for the email industry. As an open source system, KumoMTA offers flexible cloud deployment options, and direct access to the platform’s source code. It’s an approach that offers ESPs like Puresend with a long-term solution to the problem of high fees and rigid lack of integration options presented by earlier generation MTAs. Rather than bow to high prices and questionable product support, Puresend now had an opportunity to work with an MTA that could make their own solution more powerful and feature-rich than ever before.
Cliff Seltzer, Puresend’s founder, explained how Rob Bernabé, Puresend’s technical director, originally got the ball rolling with KumoMTA. “Rob is keyed into the technical email discussions happening online, the blogs and the chat boards,” Seltzer explained. “So he was keeping up with everything the Kumo team had been doing. And of course, we knew the Kumo guys going way back. So when we were first thinking about making a change, he was like, ‘You know, these Kumo guys really have something here. So we decided to move forward with KumoMTA.”
With only a two month window to switch over, Puresend discovered KumoMTA was an easy provider to work with. As an open source service, KumoMTA costs nothing to set up, with the only fees coming from direct support from the developers. For an independent ESP that needed to move quickly to keep their customer services running properly, KumoMTA proved to be the answer they were looking for.
By turning to KumoMTA, Puresend found a far better system to rebuild their business around. KumoMTA is designed for the performance needed by enterprise senders such as Puresend, which often manages sending volumes reaching up to three hundred million emails per month for their clientele. Thanks to its Lua scripting engine and support for technologies including webhooks, AMQP, Kafka, Vault, Prometheus, Grafana, and direct database access, KumoMTA was able to replace the previous MTA system set in place without any loss of functionality or interruption of service.
About KumoMTA
KumoMTA is the open-source email platform specifically designed for today’s high-volume senders. Among its key attributes:
The software is free to use, review, and modify as the user sees fit—no license fees.
Provides industry-leading performance—capable of saturating physical hardware—while ensuring that messages are safely queued to prevent loss or double-sending.
Delivers full real-time integration capabilities for configuration, message manipulation, and routing via its built-in policy engine and data source access.
Fully integrates into your DevOps environment, with a containers, and native support for both SOCKS5 and HAProxy forward proxies.
Backed by a 24/7 response SLA available directly from the team that built it.
The Results - A Stable Present, a Promising Future
Released under the Apache 2 OSI-approved license, KumoMTA is transparent with its systems and source code, which is hosted on Github. It has an active community involved and contributing to the MTA, ensuring improvements for companies looking to remain independent. Altogether, these services and support allowed the integration of already present configurations in Puresend’s systems, ensuring an easy transition between services.
As Rob Bernabé puts it: “It was a two-month sprint to get Kumo in place and avoid having our business go dark. So it was super fast for both us and the Kumo team. The Purecast platform is somewhat complicated, but we were able to handoff our previous MTA configurations and we went from there. There was a lot of tweaking and adjustments to get it going, and we were really down to the wire–full nights, long phone calls. But, you know, the Kumo team was there for us.”
A key difference with KumoMTA is that it gives ESPs like Puresend much more control over not just their infrastructure, but business maneuverability also. As Puresend’s experience shows, with legacy MTAs, you're not in control of pricing, licensing, feature sets, future roadmap of the product, and so forth. In order to control how these legacy servers behave, you have to build around its distinct idiom. Even with SaaS / cloud MTA offerings, senders have limited control. You can still face price shocks, and have to contend with technical issues like lack of control over traffic shaping. Additionally with conventional SaaS services, if the platform goes down, you’re basically dead in the water waiting for the system to come back online.
With KumoMTA, the customer is in control. Customers like Puresend aren’t forced into a closed license where their servers could go down if they don't pay their bill. Additionally, Kumo’s Lua policy engine provides tremendous flexibility. Configuration is managed via code, so control over basic MTA configuration is all handled in-house. Installing on-prem means Kumo customers control their own fate.
Bernabé continued: “We were actually quite concerned about deliverability, and we wanted to make sure that there were no sudden changes in terms of sending speeds and throttles. We wanted to make sure that the configs would be exactly identical so that there wouldn't be an impact when we did this transition because of the concern about deliverability. So credit to the Kumo guys for helping that not be impactful in that way.”
With the benefits of experienced developers on their side to set up the services they needed, Puresend was able to transition from their former MTA to Kumo without any long-term problems with their business. As explained by Cliff Seltzer, “We had some scary times and some hiccups, but the Kumo guys stood behind their solution. It could have been very easy for them to just throw up their hands, but they stood behind us and got us there.”
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