Write formatted mail
Bold, italic, colours, both kinds of lists, quotes, links and a table, in a composer that sends a plain-text part with every formatted message.
Free and open source · GPL-3.0-or-later
A small, fast email client for Windows.
Komorebi reads and writes mail without getting in the way. It keeps a local SQLite cache of your IMAP mail, draws HTML mail with its own layout engine and looks like the rest of Windows 11. No AI, no telemetry, no web engine.
Everything mail needs, nothing it does not
One native program for Windows 10 and 11, in English and European Portuguese.
Reads mail, not trackers
HTML mail is drawn by Komorebi's own layout engine, with no scripts and no web engine. Remote images wait until you choose to load them, and tracking pixels never load.
A rich-text composer
Email-safe fonts and sizes, ten named colours, lists, quotes, links and simple tables, with named signatures. Mail with no formatting goes out as plain text.
Recipients as chips
Addresses turn into chips as you type, a wrong one is flagged before you send, and suggestions come from your contacts first.
Contacts with CardDAV
A local address book with groups, synced per account over CardDAV if you want it, read only or read and write.
Calendar with CalDAV
Month, week, day and agenda views, an event editor, invitations you can answer and your accounts' CalDAV calendars. Reminders are opt-in.
Rules, and Copy as Sieve
Simple local rules for new Inbox mail: move, delete, mark read or important. Copy them as a Sieve script for your provider's filters.
Tabs and windows
Open messages in tabs or in windows of their own to read side by side. Open tabs come back at the next start.
Your provider or your own server
Presets for Purelymail and Postale.io, any IMAP and SMTP server by hand, certificate pinning for self-signed servers and SMTP without sign-in for a local relay.
Notifications and tray
Windows notifications for new mail and event reminders, a notification-area icon and start with Windows. All off until you turn them on.
A closer look
Your calendar beside your mail
A local calendar on this PC and your CalDAV calendars, in month, week, day and agenda views. Changes go to the server only over the version you edited.
Rules that stay on your computer
Each account has an ordered list of rules for new Inbox mail. An activity list shows what they did, and no rule ever sends mail.
Pin your own server's certificate
For a self-signed or private-CA server, review the SHA-256 fingerprint and trust that certificate, its key or its issuing CA. A changed certificate is refused before any password is sent.
Small and quick, by design
The project holds itself to written budgets, checked with the app's own timing switch on a seeded cache.
- < 200 ms
- budget from start to the first window; about 40 to 60 ms measured on a quiet machine
- < 600 ms
- budget to list a cached folder
- 8.9 MB
- installer of the latest release
- 0
- telemetry, analytics or crash reports sent anywhere
Timings depend on your computer and disk; a first start after installing can be slower.
What leaves your computer
There is no Komorebi server. The app connects only to:
- your mail servers (IMAP and SMTP, always over TLS or STARTTLS), and the CardDAV and CalDAV servers you set up;
- your mail domain's DNS and autoconfig page, only when you press Continue or Find settings for a domain without built-in settings;
- the image hosts of a message, only after you choose to load its images;
- api.github.com and github.com, only when you check for updates or download one.
Open about how it is built
Verified updates
The in-app update installs a new version only if its SHA-256 matches and its Ed25519 signature verifies against a key built into Komorebi.
Code signing
Releases are not Authenticode-signed yet. An application to SignPath Foundation for free code signing is in progress.
Source you can build
Rust and Slint, GPL-3.0-or-later. Clone the repository and build the same single komorebi.exe with Cargo.
Try Komorebi
Installs for your Windows user, with no administrator rights, and uninstalls from Settings > Apps.