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This article is based on comments gathered from Benoît Tellier, Tech Lead Twake Mail at LINAGORA.
In the development of Twake Mail, LINAGORA’s collaborative messaging platform, performance is a central concern. Yet, when trying to precisely measure the behavior of our architectures based on Apache James and modern protocols such as JMAP, our teams encountered an unexpected finding: there was no truly suitable tool to carry out realistic, reproducible and automatable IMAP benchmarks. At FOSDEM 2026, Benoît Tellier, Tech Lead on Twake Mail, presented how LINAGORA filled this gap with gatling‑imap, an open‑source connector that finally brings an industrial framework to email performance testing.
1. Twake Mail, JMAP and Apache James: performance as a continuous requirement
Twake Mail is the collaborative messaging solution developed by LINAGORA. It combines a modern web client with a robust server architecture, designed to meet today’s demands for collaboration and digital sovereignty. The platform relies notably on JMAP, a protocol conceived to modernize email exchanges, and on Apache James, a reference open‑source mail server to which LINAGORA has been contributing actively for several years.
In such an environment, performance is not merely a comfort metric. It directly conditions the quality of service, the ability to absorb load, and the reliability of deployments for our customers. Every code change, every optimisation of the server or integration layers must be evaluated objectively. The stakes are twofold: validating our architectural choices and securing production releases with measurable data.
To achieve this, we need reproducible benchmarks capable of simulating realistic loads and delivering clear metrics. Unfortunately, this is precisely where a gap appeared.
2. IMAP: a central protocol… but poorly served by testing tools
While the HTTP‑API ecosystem today enjoys very mature performance‑testing tools, the situation is quite different on the mail side. IMAP remains a central protocol in many email architectures, even in modern environments where it coexists with JMAP.
Existing IMAP testing tools are often partial, poorly maintained, or hard to integrate into automation pipelines. They may replay a few commands, but they struggle to describe scenarios close to real‑world usage. Yet an email user does not simply open a connection: they navigate between folders, read messages, receive new ones, and change the state of their mailbox. This succession of actions creates the actual load on a server.
For the teams working on Twake Mail and Apache James, this made it difficult to set up an automated, comprehensible IMAP benchmark that the whole team could understand. Without a common framework, it becomes cumbersome to compare performance over time, measure the precise impact of a fix, or quickly detect a regression.
3. Gatling‑IMAP: a modern DSL for reproducible IMAP benchmarks
To meet this need, LINAGORA’s teams chose to build on Gatling, an open‑source performance‑testing and load‑testing tool widely used in the industry. Gatling is based on a declarative DSL in Scala, allowing complex scenarios to be described in a readable way while producing detailed charts and exploitable statistical summaries.
This framework matched the expectations perfectly: expressiveness, automation, and clear metrics. It simply lacked the ability to talk to an IMAP server. This led to the development of gatling‑imap, a connector that adapts Gatling to the IMAP protocol and enables the construction of test scenarios representative of real‑world mail usage.
With gatling‑imap, scenarios become version‑controlled artifacts, integrable into continuous‑integration pipelines. They can be replayed identically to compare different server versions, validate the effect of an optimisation, or objectively assess the impact of an architectural change. The results, presented as graphs and detailed statistical summaries, make analyses accessible far beyond performance specialists.
For Twake Mail, this is a direct lever to maintain a high level of service quality and performance. For Apache James, it adds another tool to evaluate evolutions and secure contributions. And for the broader mail ecosystem, it provides an open‑source IMAP driver that fills a long‑standing gap.
Benoît Tellier, mail‑solutions architect at LINAGORA, presented this approach during the Modern Email devroom at FOSDEM 2026. His experience illustrates how a concrete performance‑validation need can blossom into an open‑source contribution useful to an entire sector.
Conclusion
As mail platforms evolve toward more modern architectures that combine JMAP, IMAP and distributed components, the ability to measure their behaviour precisely becomes strategic. Performance can no longer be evaluated sporadically or empirically; it must be embedded in a continuous process based on reproducible benchmarks and reliable metrics.
With gatling‑imap, LINAGORA adds an essential building block to the tooling landscape, enabling IMAP tests to benefit from modern web‑testing standards: DSL‑described scenarios, automated execution, and detailed reports. This concrete contribution benefits Twake Mail, Apache James, and the whole email community.
The project is open source and available on GitHub
Are you working on mail infrastructures and want to objectify your IMAP performance tests? Try gatling‑imap and help advance modern mail tooling.
Finally, to dive deeper into the technical challenges and see the full experience presented at FOSDEM by Benoît Tellier, the conference video is available here
