Seven substantial pieces of software power email.eu and we wrote almost none of them. Stalwart, Bulwark, La Suite Drive, Zulip, La Suite Meet, Authentik and Lago: the four tests every component had to pass, and the choices we got wrong first.
When you sign in to email.eu you see one product: mail, calendar, files, docs, chat and video meetings behind a single login. Under the hood it's seven substantial pieces of software, and we wrote almost none of them. This post is about what we picked, what we rejected, and the criteria that did the picking. It's part 2 of our series on how we built email.eu; part 1 explains the supplier rule that shaped every choice below.
Every component had to pass the same four tests.
Here's how that played out, pillar by pillar, including the choices we got wrong first.
The heart of the product. Stalwart is a modern mail server written in Rust that does SMTP, IMAP and JMAP in one coherent system, with clustering built in, instead of the traditional stack of five separate daemons wired together with folklore. It's the kind of choice that would have been risky five years ago and felt obvious by the time we committed. We run it as a two-node cluster and pay for the enterprise license. Part 3 of this series is entirely about running it in production.
We launched on Roundcube, the safe default, and replaced it within weeks. Bulwark is a newer open-source webmail that talks JMAP rather than IMAP, which makes it feel like an app instead of a webpage that reloads, and it brings calendar and contacts along in the same interface. Your calendars and address books are ordinary CalDAV and CardDAV data underneath, so any desktop or phone client syncs against the same account. We've sent patches upstream where we hit rough edges, which is what test four looks like in practice when there's no invoice to pay.
La Suite Drive handles file storage and sharing. Like Meet below, it comes out of La Suite, the French state's open-source workspace effort, and every customer gets their own isolated instance of it rather than a folder in a shared one. ONLYOFFICE provides document editing in the browser, connected over WOPI, the open document-editing protocol. The deciding feature was covered in an earlier post: documents are stored as real .docx, .xlsx and .pptx files from the moment you create them. Nothing proprietary goes in, so nothing has to be converted on the way out.
Zulip is team chat with threading that actually works, and, decisive for us, first-class support for running many isolated organisations on one installation. Every customer gets their own realm with its own users, its own history and its own sign-in wired to their email.eu account.
Our most public wrong turn. We spent real time on a Matrix and Element Call setup before admitting it wasn't going to reach the reliability a business customer expects from a "join meeting" button. We threw it away and moved to La Suite Meet, the video-conferencing stack from the same French workspace effort as our Drive, running on LiveKit. It worked, guest links and all, within days of the pivot. The lesson we took: when a component fights you for weeks, the sunk cost is the warning, not the reason to continue.
The pillar we churned on most, because everything else hangs off it. We evaluated and partially deployed two other identity systems before converging on Authentik, which now provides single sign-on for the web apps and a directory for the mail server, per customer, from one place. That story, and why the login service gets treated as production-critical as mail, is part 4.
Lago is an open-source billing engine we self-host; Mollie, from Amsterdam, processes the payments. Card numbers go to Mollie directly and never touch our systems. Per-seat billing, proration and dunning are exactly the kind of logic you should not hand-roll next to your own invoices.
The one piece we built from scratch is the control plane at app.email.eu: signup, domain management, team management, billing screens, support, and the provisioning machinery that turns "new customer" into accounts across everything above. That's part 7.
Which brings up the question we get asked most on this subject: is email.eu open source? The honest answer is that the product is not, and the building blocks largely are. Everything your data lives in (the mail server, the file store, the identity provider) is open-source software you could run yourself, storing your data in open formats behind open protocols. The glue that makes it a hosted product is ours. We fund and contribute to the projects we build on, because their health is our health. We'd rather state that plainly than stretch the term.
Next up, part 3: what it takes to run your own mail servers in 2026, and why almost nobody should but somebody has to.