A mail cluster spends its day asking small questions: is this message locked, has this client hit its limit, did anything change? Stalwart Keep is the server we built to answer them. It replaces Redis and a message broker with one service, finishes 99% of requests within 59 microseconds at a large deployment’s typical load, and has been through Jepsen.
The first of the features held back from the v1.0 cut is here. Stalwart v1.0.2 introduces an encryption gateway that encrypts outgoing mail for its recipients, a new OpenPGP and S/MIME engine with modern and post-quantum algorithms, and a restyled WebUI. Everything in this post is open source.
Five years ago, on 3 October 2021, the first commit landed in a small repository called mail-parser. That e-mail parsing library became the seed of a complete mail and collaboration server, and today, after five years of continuous development, we are proud to announce Stalwart v1.0, the first stable release.
Version 1.0 is about two things: speed and stability. We spent months profiling, benchmarking and rewriting the hot paths of the server, and the result is a mail server that outperforms the Postfix and Dovecot combination in 35 of 38 head-to-head benchmarks. We also finalised the database schema, so future releases will no longer require disruptive migrations.
Open source works because it is a relationship that benefits both sides. Lately, a few actors have started treating Stalwart as something to feed on instead. This post explains what has been happening, why our test suites are moving to a private repository, why the license is not changing, and how the Enterprise edition keeps the Community edition alive.
Sieve has no statement for printing a value or writing to a log, so debugging a mail filter has long meant sending test messages and reading debug headers out of their raw source. Sievepad runs the Stalwart Sieve interpreter in the browser, inside the editor that powers Visual Studio Code, so a script can be written, run and debugged against test messages in seconds, without a server and without sending a single email.
