A two-person Dutch ESP built a sending stack on European soil, on open source, with no investors. The one US supplier left standing handles the billing.
Lettermint is a transactional email provider based in the Netherlands. It pitches itself as a sovereign alternative to Postmark and Resend for developers who want password resets and order confirmations to stay inside EU jurisdiction. It runs on KumoMTA, monitors through Postmastery Console, and both vendors have published their own case studies. Those are worth reading. We spoke to co-founder Bjarn Bronsveld for the version without a sales objective.
It started as a joke
The idea came out of Postmark’s acquisition by ActiveCampaign. Developers in Bronsveld’s community were unhappy, and the running joke was that they should build their own. “That’s of course a bigger challenge than you always think,” he says. The idea was parked.
It came back as the 2024 US election approached and the EU sovereignty conversation got louder. By November 2024 the two founders were building. “When the inauguration took place in January, we were like, well, there’s really something for this.” European competitors existed, but Bronsveld points out most of them sat on AWS or Google Cloud. Lettermint launched at the end of May 2025.
Postfix lasted about two months
With no budget, the first MTA was Postfix. It did not scale and it slowed development. Bronsveld found KumoMTA in early 2025 and read the whole documentation site, which he says was a first. He and his co-founder then spent one day in the office standing it up, feedback loops included, and sent their first message from it. They launched on Kumo and have expanded the integration ever since.
Bronsveld makes a monthly personal donation to the project through its Discord. He wants to give more once Lettermint pays two salaries. It currently pays none. Both founders still have day jobs.
Postmastery arrived in September 2025. Before that, bounces and complaints were read by hand, which Bronsveld describes as the fastest route to launch and a way of knowing everything that was happening. He assumed an undisclosed price meant an expensive one. It did not. The console now handles the monitoring and the two companies check in every few months.
What sovereign means here
Bronsveld’s definition is short: all customer data in one jurisdiction, and that jurisdiction is the EU. KumoMTA’s own follow-up post separates residency from sovereignty on the same basis. A Frankfurt data centre owned by a US company is still reachable under the CLOUD Act.
Lettermint holds its own IP space and runs its own network, so reputation stays inside it. Compute is with UpCloud, a Finnish provider, in a Dutch data centre. Backups sit with OVHcloud in Germany. Transactional and broadcast traffic are separated at the infrastructure level. If UpCloud receives a subpoena, that is a matter for Finnish and EU law.
The exception is Stripe. Bronsveld calls it the one supplier they feel bad about. There is no comparable European alternative for card billing yet, so the compromise is to give Stripe nothing beyond a billing contact and invoices. No customer email data crosses that line. Few vendors name their gaps at all.
Tracking, with an off switch
Open and click tracking is available however off by default. When the French and Italian regulators published their views on tracking pixels, Lettermint added a per-message toggle, via the API or SMTP headers, so a sender can disable tracking for one recipient and keep it for another. Bronsveld compares it to a cookie banner.
The hard part is trust
Lua was easy enough; Bronsveld had used it years ago for game mods. The MTA was a day’s work. Trust takes years. Nobody hands critical infrastructure to a company with a short track record, and Bronsveld considers transactional email critical infrastructure: if the magic link does not arrive, nobody logs in. Early customers were freelancers and small agencies. Larger ones came later, some with long compliance questionnaires and a clear demand for a sovereign supplier. Most, he admits, just want a platform that works.
Would Lettermint exist without the sovereignty debate? He is not sure it would have started when it did. He would build it now regardless, because he is enjoying it.
We asked what happens if KumoMTA vanished tomorrow. It is open source, so the software would not vanish with it. Bronsveld’s answer was that Kumo taught them how an MTA works, they have read the source and filed bugs, and any move to a commercial MTA would come down to licence fees. He mentioned PowerMTA, and its price, in the same sentence.
We did not ask for volume or latency figures. Lettermint is a small private company and there is nothing independent to compare them against. Kumo’s case study reports a hundredfold growth to around 200,000 messages a day; treat that as a company figure.
Disclosure: KumoMTA is an emailexpert enterprise member and Postmastery is a strategic partner. The interview was conducted by video call on 24 August 2026 and recorded with an AI notetaker. Quotes have been lightly tidied from the transcript and checked with Lettermint before publication.
Sep 10: Article corrected to note that tracking is OFF not On by default.
