Leboncoin | Migrating a legacy email infrastructure to PowerMTA on AWS
"Migrating a sending infrastructure of this scale takes method, the right tools, and the right partners. PowerMTA gave us the operational control and visibility we were missing, and Postmastery's support — both on configuration and on deliverability — allowed us to run this project from end to end with confidence."
Case study with: Edouard Perret & Marie Doulliet
Infrastructure Engineer & Engineering Manager at Leboncoin
About Leboncoin
Leboncoin is France's leading classified ads marketplace and the country's second most visited e-commerce site. The platform hosts 89 million active ads at any time, draws 30 million unique visitors every month, and enabled the exchange of 153 million items last year. More than one in two French internet users rely on it. Leboncoin is part of the Adevinta group, which operates more than 25 marketplaces worldwide.
Email is a critical channel for the platform: it runs across the entire user journey, from transactional notifications to messaging between buyers and sellers.
The starting point
In 2024, Leboncoin handled a volume of 4 billion outbound emails per year, split between 58% transactional emails and 42% messaging emails. The infrastructure was running on 20 Postfix servers managed via Puppet, hosted in the group's datacenter — while 99% of the rest of the infrastructure was already on AWS.
This legacy setup carried a concentrated operational risk on several fronts:
- Aging infrastructure.
- Dependency on a configuration tooling reaching end of life at Leboncoin.
- Limited internal technical knowledge of the scope, due to various company reorganisations.
On top of that, requirements from major mailbox providers around compliance, reputation, and sending quality have tightened noticeably over the period.
Against this backdrop, Leboncoin's Infrastructure team launched a complete redesign of the sending chain.
Choosing PowerMTA
The team carried out an assessment of the available market solutions in light of the volumes handled, reliability requirements, and deliverability goals. PowerMTA stood out across six key dimensions:
- Delivery performance and ability to scale.
- Granular throttling and optimisation by ISP, domain, and route.
- Advanced IP and traffic management.
- Native handling of bounces, deferrals, and feedback loops.
- Stronger observability and operational control through API and UI.
- Resilient queue management with backoff and failover mechanisms.
To frame the project, Leboncoin relied on Postmastery's support, the historical PowerMTA partner in France.
The target architecture
The legacy architecture relied on a Messaging Servers → Postfix Messaging (6 VM) → Haproxy Pool (5 VM) → Postfix MTA (20 VM) chain, terminating in the datacenter before delivery to recipients.
The target architecture moves the entire email sending chain to AWS: email-producing applications hosted on an EKS cluster feed a Network Load Balancer, which distributes email traffic to a PowerMTA cluster configured with 3 × 7 IPs. Outbound traffic now goes directly from AWS to recipients.
This target addresses three objectives: align the email infrastructure with the rest of the cloud stack (move out of the datacenters), reduce the operational surface, and give email-sending teams fine-grained IP isolation per use case.
Real-time visibility through the Postmastery Console
Beyond the MTA choice and the consulting service, Leboncoin wanted an independent monitoring tool to track sending performance continuously. The Postmastery Console was deployed in parallel with the project, giving the teams direct access to deliverability indicators and real-time log analysis.
During the migration phase, the Console played a key role: tracking IP warm-ups batch by batch, early detection of weak signals (slowdowns, bounce or complaint spikes), and the ability to quickly compare performance between old and new IPs. This shared visibility allowed Leboncoin and Postmastery teams to make decisions faster and with more confidence at each step of the rollout.
Once the migration was complete, the Console became the daily steering tool for deliverability: real-time dashboards, alerting, filtering by domain, by IP, and by use case, and a usable history for trend analysis. The Leboncoin teams have gained autonomy on operational analysis, while keeping access to Postmastery's expertise for more complex cases.
Migration timeline
The migration ran from April to December, with a progressive approach to limit risks:
- April → August - Release of the datacenter IPs and preparation of the transfer.
- September 2nd - IP transfer to AWS.
- September → November - Three successive warm-up batches, with progressive traffic ramp-up on the new IPs.
- December 11th - Postfix decommissioning.
Throughout the project, Postmastery supported the Leboncoin teams on PowerMTA configuration, deliverability advice, incident support, and connecting them with the right contacts when needed.
Results
Following the migration, the results measured in March 2026 are as follows:
- 343 million emails submitted over the measured period
- Bounce rate: 0.8% - down by 0.4 points
- Complaint rate: 0.02%
- Spam trap rate: 0.00% (1,679 absolute hits)
- Average delivery time: 3 seconds
- Infrastructure cost: $1,800 / year on PowerMTA, versus an estimated $14,000 / year for an equivalent infrastructure based on Postfix servers on AWS - roughly an 87% reduction
Beyond the numbers, the migration brings structural benefits: IP isolation per use case, native metrics on asynchronous bounces and feedback loops, simplified bounce categorisation, and stronger operational confidence across the chain.
What's next
Building on this new infrastructure, the Leboncoin team is now exploring projects at the intersection of infrastructure and product, in particular around product governance applied to email - to better manage email spikes triggered by certain business scenarios and preserve the platform's overall deliverability.
"Migrating a sending infrastructure of this scale takes method, the right tools, and the right partners. PowerMTA gave us the operational control and visibility we were missing, and Postmastery's support — both on configuration and on deliverability — allowed us to run this project from end to end with confidence."
| Edouard Perret, Infrastructure Engineer & Marie Doulliet, Engineering Manager at Leboncoin
About Postmastery
Postmastery helps legitimate senders be recognised as trusted senders and reach the inbox. Our client base includes email service providers (ESPs), marketing agencies, and demanding professional senders. Postmastery is a global partner of leading MTA vendors - PowerMTA, GreenArrow, Halon, KumoMTA, Postfix - and offers integration services, local support, and deliverability optimisation.