Stalwart vs Mailu

Stalwart and Mailu both let you run your own email without committing to Mailcow's heavyweight groupware stack, and both are credible, lightweight choices. But they get there from opposite directions. Stalwart is a single Rust binary that does SMTP, IMAP, JMAP, and CalDAV/CardDAV in one process with a built-in admin UI baked into the binary itself. Mailu is a small suite of Docker images — an admin app, a database, mail daemons, antispam, and bundled webmail — generated by a setup wizard into a docker-compose stack you run yourself. One is a modern rewrite that fits in one file; the other is a friendlier assembly of the classic pieces.

One Rust binary vs. a wizard-built compose suite

Stalwart rebuilds the mail stack from scratch in Rust. SMTP, IMAP, JMAP, and CalDAV/CardDAV all live inside the same executable, and its admin UI ships with it — there's no separate MTA, IMAP daemon, or database engine to wire together. Point DNS at it, start the container, and the whole server is one thing to patch, back up, and reason about.

Mailu takes the more familiar Docker Compose route. You run its setup wizard at setup.mailu.io, which generates a docker-compose.yml and an env file tailored to your choices, then bring up several coordinated services — a Flask-based admin app, a database, the mail daemons, Rspamd for antispam, and bundled Roundcube or SnappyMail webmail. Day to day, you manage users, aliases, and domains from that web admin panel rather than editing files. It's a gentler on-ramp than assembling Postfix and Dovecot by hand, without committing to Mailcow's full groupware layer.

Footprint

The documented minimums look close on paper — Stalwart and Mailu both cite roughly 1 GB of RAM as their floor — but that similarity doesn't survive contact with a real box. Stalwart is unattended-installable, so it has a measured number: a fresh instance idles at ~10 MB at first boot, well under its own documented floor and comfortably inside the smallest VPS tiers. Mailu has no equivalent measured figure, because its install has no unattended path — the wizard at setup.mailu.io is interactive by design, so there's nothing to run a clean first-boot measurement against. Its own docs cite 1 GB as the floor for the admin app, database, and webmail combined, and that documented number is the honest one to plan around rather than assuming Mailu will match Stalwart's measured idle figure just because their published minimums match.

Either way you frame it, Stalwart's single binary is the lighter of the two — a measured ~10 MB against Mailu's documented 1 GB is close to two orders of magnitude, even before Mailu's admin app and webmail start doing real work.

Protocols: Stalwart's JMAP is the differentiator

This is Stalwart's clearest edge over Mailu, not just a footprint story. JMAP is a modern, efficient HTTP/JSON sync protocol designed to succeed IMAP's older round-trip model, and Stalwart implements it as a first-class citizen alongside CalDAV/CardDAV for calendars and contacts. Mailu's fixture and docs describe SMTP and IMAP with webmail on top — there's no JMAP support and no CalDAV/CardDAV layer to speak of. If you want your mail server itself to speak the newest protocol, or plan to build a JMAP client against it, Stalwart is the only one of these two that offers that path.

Webmail: the one place Mailu wins outright

Stalwart deliberately stops at the server boundary — no bundled webmail, just IMAP and JMAP for you to point Thunderbird, Apple Mail, or any other client at, with a separate tool like Roundcube if you want browser access. Mailu ships Roundcube or SnappyMail out of the box, so a user gets a working inbox in a browser the moment their account exists, with zero extra setup. For anyone who wants that turnkey experience for non-technical users without standing up a second piece of software, this is Mailu's real advantage, and it's the one place the smaller, lighter Stalwart genuinely loses.

Setup and administration

Stalwart's install is a single container: pull the image, mount two volumes, start it, and grab the one-time admin password from the container logs to finish setup in its built-in web UI. There's no wizard step and no separate generator script — the binary is the whole product.

Mailu's setup starts outside the server entirely, at the setup.mailu.io wizard, which walks you through domains, features, and passwords before handing you the compose file and env file to deploy. That extra step is friendlier for people who'd rather answer questions than read documentation, but it also means Mailu can't be stood up with one unattended command the way Stalwart can. Both rate 4 out of 5 to deploy — Stalwart's difficulty is in correctly wiring DNS and TLS around a single binary with a lot of ports open, Mailu's is in getting the wizard's choices and the resulting compose file right the first time.

Which to choose

Choose Stalwart if footprint and modern protocols matter most — a single binary that measures ~10 MB idle, ships JMAP and CalDAV/CardDAV, and is comfortable running on the smallest VPS tier, at the cost of bringing your own webmail. Choose Mailu if you want a guided setup wizard, a web admin panel, and working browser-based webmail from the moment you deploy, and JMAP isn't something you need.

Not the only two options

Stalwart and Mailu are both lightweight compared to a full groupware suite, but they aren't the only lightweight options, and the other two apps in this cluster are worth a look before you commit. Mailcow sits at the heavy, complete end of the spectrum — SOGo webmail, ActiveSync, and a polished admin UI, at the cost of a measured ~2.2 GB idle footprint and a documented 6 GB minimum; see our Stalwart vs Mailcow comparison for that angle specifically. docker-mailserver sits close to Stalwart on RAM but takes a completely config-file-driven, no-UI approach instead of Stalwart's built-in admin panel; our Mailu vs docker-mailserver comparison covers that exact "web panel vs. config files" trade-off directly.

Who should pick neither

If what you actually want is Mailu's friendly wizard and bundled webmail but running on even less RAM than its documented 1 GB floor, or you want Stalwart's single-binary simplicity but with SOGo-style groupware built in, neither of these is quite the fit — read the Mailu vs docker-mailserver and Stalwart vs Mailcow comparisons to see where the other two members of this cluster land on those same trade-offs.

Choosing between Mailu and Stalwart

Reversed, the decision is the same trade-off restated: pick Mailu first only if a setup wizard, a web admin panel, and bundled webmail are requirements you don't want to solve yourself, and JMAP isn't on your list. Otherwise, default to Stalwart — a measured ~10 MB idle footprint, a single binary to patch and back up, and JMAP and CalDAV/CardDAV alongside the SMTP/IMAP classics, at the cost of bringing your own mail client or webmail.

The part neither solves: deliverability

One caveat outweighs the software choice entirely. The hard part of self-hosting email isn't the server — it's convincing the rest of the internet to trust it. Whichever of these you pick, you still need a clean sending IP with a good reputation, a correct reverse-DNS (PTR) record, and properly configured SPF, DKIM, and DMARC. Get those wrong and your mail lands in spam no matter how modern or how friendly the software is. Budget as much time for DNS and reputation as for the install itself — that, far more than the Stalwart-versus-Mailu decision, determines whether self-hosted email actually works for you.

A note on licensing

One more thing worth flagging plainly before you pick: Stalwart's Community Edition is licensed AGPL-3.0, a copyleft license with network-use disclosure obligations — if you modify Stalwart and offer the modified version as a service to others, you're expected to release those changes. Stalwart also offers a separate proprietary Enterprise license for organizations that need different terms. Mailu is MIT-licensed, with no such obligations attached. For most self-hosters running mail for themselves or a small team, AGPL is rarely a practical blocker, but it's a real consideration if you plan to build a commercial hosted product on top of either one.