KUMO CASE STUDY

How Laposta achieved 2-3× faster throughput and 90% IP reduction with KumoMTA

Laposta is a Netherlands-based email service provider whose intuitive platform powers newsletters for more than 60% of Dutch municipalities, major hospitals, non-profits, and e-commerce brands. Each month, it delivers millions of messages, from critical civic alerts to high-volume marketing campaigns, where reliability, speed, and inbox placement are paramount.

As a mission-critical service provider handling diverse email workloads, Laposta required robust mail transfer agent (MTA) infrastructure capable of high-volume delivery while maintaining excellent deliverability rates. When the company’s aging Postfix infrastructure approached end-of-life and operational limitations became increasingly apparent, Laposta partnered with our authorized Europe-based support provider of KumoMTA, Postmastery, to evaluate modern alternatives and execute a strategic infrastructure migration.

The Challenge—Aging Infrastructure Meets Growing Complexity

Laposta’s email infrastructure had grown organically over the years into a complex web of three Ubuntu/Postfix virtual machines hosting more than 200 Postfix instances across 200 IP addresses. This architecture, while functional, presented multiple challenges that threatened the company’s ability to serve its customers effectively.

From an operational perspective, the infrastructure was approaching a critical juncture. The underlying Ubuntu operating system was scheduled to reach end-of-life around mid-2025, forcing a decision: upgrade the entire complex stack or migrate to a new platform entirely. “We saw mixed signals in Gmail’s dashboard but didn't necessarily know why, or how to fix them quickly,” explained Stijn van der Ree, Laposta’s founder. “What we did understand clearly is that we had a lot of limitations with our legacy setup.”

The visibility problem was pervasive. Troubleshooting delivery issues required manually grep-searching through logs across hundreds of Postfix instances, with no centralized dashboard or monitoring capability. “Postfix provides little visibility—it was difficult to understand where problems were arising from,” van der Ree noted.

Beyond visibility, the architecture lacked modern email delivery capabilities that had become essential for maintaining sender reputation in today’s email ecosystem. The infrastructure was missing critical features like advanced transport rules, connection reuse, DSN rewrite capabilities, and custom retry logic. These limitations meant aggressive retries and potential reputation impacts that could affect deliverability across their entire customer base.

The scaling challenge was equally significant. The multi-instance architecture struggled to efficiently handle growth, and the prospect of aligning all versions of Postfix across hundreds of instances represented a massive undertaking. As Yves-Marie from Postmastery observed during the initial assessment, “the La Posta infrastructure was sited on three virtual machines (VMs) with hundreds of Postfix instances on each. Aligning all versions of Postfix was going to be a huge undertaking.”

"Open source was an appealing feature for us — peace of mind that access to the code is open-ended."

— STIJN VAN DER REE, LAPOSTA

Perhaps most critically, deep MTA-level expertise was rare and expensive. While deliverability was mission-critical to Laposta's business, maintaining the specialized knowledge required to operate and optimize hundreds of Postfix instances at scale was becoming increasingly unsustainable.

The Solution: Migration to KumoMTA Guided through the Postmastery Console

Recognizing the complexity of their infrastructure challenge, Laposta engaged Postmastery, a support provider of KumoMTA, to conduct a comprehensive delivery assessment and guide their infrastructure modernization. This partnership brought deep MTA expertise to bear on evaluating options and executing the migration.

Postmastery’s evaluation process considered multiple MTA platforms, including PowerMTA and KumoMTA. The open-source nature of KumoMTA proved decisive. “Open source was an appealing feature for us—peace of mind that access to the code is open-ended,” explained van der Ree. The team also appreciated the people and community behind the project: “We felt good about the people behind Kumo—lots of good energy and strong use cases coming through from your website.”

The migration followed a methodical, phased approach that minimized risk while delivering progressive improvements:

Step 1: Baseline and Prototype

Postmastery instrumented the legacy Postfix stack to capture detailed deferral and bounce patterns, establishing performance and deliverability baselines. A single-IP KumoMTA prototype was built, including a custom MySQL-based DKIM key manager to replicate OpenDKIM functionality while providing the flexibility needed for Laposta’s multi-tenant environment.

Step 2: Feature Expansion and First Migration

The platform was enhanced with production-critical features, including DKIM oversigning, feedback-loop management, throttling optimization, rewrite-rule management, bounce classification, and resource optimization. The first /24 IP block was migrated, and a From-domain-based feedback loop DKIM scheme was introduced to improve complaint tracking and sender identification.

Step 3: Validation and Parallel Operation

Performance and deliverability metrics were rigorously benchmarked between the legacy Postfix infrastructure and the new KumoMTA deployment before proceeding with final cutover. This validation phase ensured no degradation in service quality during the transition.

Step 4: Replication and Consolidation

A second KumoMTA instance was deployed for redundancy, and all remaining IPs were migrated. A central suppression list feature was added to eliminate repeated delivery attempts to full or invalid mailboxes, further improving efficiency and sender reputation.

Step 5: Optimization and Handover

The legacy infrastructure, consisting of three VMs, 200 IPs, and hundreds of Postfix instances, was dramatically consolidated to just two VMs, 16 IPs, and two KumoMTA instances. The entire migration and tuning process was completed in approximately six weeks—an extraordinarily fast timeline for a transformation of this scope.

The Results—Dramatic Performance Gains and Operational Simplification

The migration to KumoMTA delivered transformative improvements across every dimension of Laposta’s email infrastructure, from raw performance metrics to operational efficiency and strategic capabilities.

Performance and Efficiency Gains

Performance improvements were immediate and substantial. Laposta achieved 2-3× faster throughput, processing the same email workload in one-third the time. This speed increase directly translated to better service for customers, with emails reaching recipients faster and campaigns completing more quickly.

The infrastructure consolidation was equally impressive. By reducing from 200 IPs to just 16 IPs—a greater than 90% reduction—without any loss in capacity, Laposta achieved dramatic simplification. The reduction from three VMs to two VMs with ample headroom for future growth delivered a 33% lower infrastructure cost.

Operational Transformation

Single-pane visibility through the Postmastery Console replaced the previous log-hunting approach. The console now surfaces per-campaign performance, deferrals, bounce patterns, and single-address traces that Laposta reviews weekly. “Support tickets fell, and client trust rose,” noted van der Ree, as proactive monitoring replaced reactive troubleshooting.

KumoMTA’s intelligent delivery features transformed how bounces and deferrals are handled. The platform performs bounce classification in-stream and feeds webhooks to Laposta for real-time reporting. Connection reuse and per-campaign deferral rules reduced infrastructure load while simultaneously boosting sender reputation.

Architectural and Strategic Benefits

The cleaner architecture delivered benefits beyond immediate performance gains. All Postfix functionality was successfully replicated via Lua scripting, with new capabilities added that were impossible in the previous environment. The smaller infrastructure footprint translated to reduced energy consumption and lower maintenance overhead, delivering sustainability gains alongside operational benefits.

Ongoing Partnership and Future Development

Postmastery continues to provide ongoing consultancy on authentication alignment, feedback loop expansion, and domain reputation optimization. The roadmap includes completing SPF, DKIM, and DMARC alignment for all customer domains before 2025 mailbox-provider mandates take effect, extending FBL coverage with dynamic suppression lists for trap avoidance, and continuing fine-tuning of throttling and resource profiles ahead of holiday peak periods.

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 rich selection of APIs, webhooks, AMQP, containers, and native support for both SOCKS5 and HAProxy forward proxies.
  
  

About Postmastery - Leading Global Email Professionals

Postmastery, a support provider of KumoMTA, is dedicated to helping senders maximize their email performance and deliverability with a range of software, tooling and consulting solutions. Offering an all-encompassing service to ensure senders can maximize performance and deliverability that includes vendor selection, MTA licensing, tuning, DMARC, training and more.

• The Postmastery Console consolidates comprehensive email delivery data in a single email analytics dashboard, delivering a clearer picture of what's really happening, enabling smarter decisions about your email delivery.
• Our global clientele includes email service providers (ESPs), marketing and advertising agencies, as well as e-commerce companies, who benefit from our vendor-agnostic, independent approach that is cost-conscious and looks to provide enterprise-grade solutions at extremely competitive price points.