Komorebi

A small, fast email client for Windows.
Read and write mail without getting in the way. No AI, no telemetry, no web engine.

Komorebi is Japanese for sunlight filtering through leaves.

What it does

• Fast and light. A window in under 200 ms (about 40 to 60 ms measured on a quiet machine), a cached folder listed in under 600 ms, and an installer of about 8.9 MB.
• IMAP and SMTP with a local SQLite cache and several accounts. Presets for Purelymail and Postale.io, manual settings for any other server, and SMTP without sign-in for a relay on your own network.
• Reads HTML mail with its own layout engine. There is no web engine, and remote content is never loaded unless you allow it.
• Writes formatted mail. Fonts, colours, lists, tables, named signatures, recipient chips, attachments and drafts.
• Tabs and separate windows, keyboard shortcuts, meeting invitations.
• Rules that file and flag mail for you, with Copy as Sieve.
• Contacts with groups and CardDAV, and a calendar with CalDAV: month, week, day and agenda views, event editing and opt-in reminders.
• Notifications and tray mode, both opt-in.
• Safe connections. Certificate pinning (exact certificate, server key or issuing CA) and an optional encrypted cache.
• English and European Portuguese, following the Windows display language.
• Signed self-updates and a per-user installer with Start menu shortcuts and a mail-client registration.

Every feature in detail: docs/FEATURES.md.

Screenshots

Inbox, remote images blocked	Rich-text composer	Calendar
Rules	Contacts	Tabs
Certificate review	Privacy settings	Welcome

The screenshots show made-up sample mail from the repository's offline test data.

Getting started

Install

1. Download the latest installer (komorebi-<version>-setup.exe, Windows 10 or 11, 64-bit) and run it. It installs for your user by default, with no administrator rights. A portable zip is on the same page.
2. Windows may show a SmartScreen warning ("Windows protected your PC"), because the installer is not code-signed yet (see Code signing policy). Choose More info, then Run anyway. You can first compare the download with SHA256SUMS on the release page.

More about the installer, silent installs, the portable zip and checksums: docs/USAGE.md.

Add an account

Start Komorebi and choose Add your email account. Enter your address and Continue: for Purelymail and Postale.io the server settings are built in, and for other domains Komorebi looks them up from your domain name (only the domain is sent, never the password). Enter your password (or an app password if your provider uses two-step sign-in); it is saved in Windows Credential Manager, never in Komorebi's files. Optionally add your name and a signature, then open your inbox. The steps in detail are in docs/USAGE.md.

Updates

You can check for updates in Settings, About, or turn on the daily automatic check (one request to GitHub for the latest release). Nothing is installed until you press Download and install, and Komorebi installs an update only if the installer matches the published SHA-256 and carries the maintainer's Ed25519 signature, which is checked against a key built into the app.

Privacy

• No telemetry, no analytics, no ads, no crash reports. There is no Komorebi service.
• Nothing is sent anywhere except to your own mail servers, a lookup of your domain's settings only when you press Continue while adding an account, and the update check to GitHub (see PRIVACY.md for each request).
• Passwords live in Windows Credential Manager. The mail cache is a local SQLite file in %LOCALAPPDATA%\komorebi, optionally encrypted.
• Remote images and other remote content in mail are not loaded unless you allow it.

The full statement is PRIVACY.md.

Code signing policy

Free code signing provided by SignPath.io, certificate by SignPath Foundation

Code signing is being set up: the application to the SignPath Foundation is in progress, and until it is approved the installer is not Authenticode-signed (SmartScreen may warn, see Install). The policy below applies to releases once signing is active.

• Roles. Author and approver: Mário Silva.
• Where releases are built. Releases are built from this repository on GitHub Actions (release.yml) and submitted for signing from there. The in-app update signature is a separate Ed25519 signature made by the maintainer on a local machine; its private key never goes to CI.
• Privacy. Komorebi does not transfer any information to other networked systems unless you ask it to. See PRIVACY.md.

How a release is made: docs/RELEASING.md.

For developers

Komorebi is written in Rust with Slint (Fluent style, software renderer), using rusqlite, imap, lettre and mail-parser.

git clone https://github.com/RusticStack/komorebi
cd komorebi
cargo build --release --locked   # target\release\komorebi.exe
cargo test --locked

Document	What is in it
docs/BUILDING.md	Build from source, the checks, verifying a build
docs/ENVIRONMENT.md	Environment variables and development switches, the offline snapshot tool
docs/FEATURES.md	Every feature in detail
docs/USAGE.md	Installing, adding an account, keyboard shortcuts
docs/TRANSLATIONS.md	Adding and checking translations
docs/RELEASING.md	The release and signing flow
docs/SCOPE.md	What Komorebi will and will not do
CONTRIBUTING.md	How to contribute
CHANGELOG.md	Changes by version
SECURITY.md	Reporting a vulnerability

Found a bug or have an idea? Open an issue.

License

GPL-3.0-or-later (LICENSE). Third-party notices are in NOTICE. Slint is used under its GPL-3.0 option; its attribution still appears in Settings, About.