The open-source Outlook alternative for Linux, Windows and macOS

Quatrelle is a free email client with a calendar, people and tasks beside it, written in Rust. Folders, a message list grouped by date, a reading pane, the ribbon and the shortcuts you already know — over IMAP and SMTP, JMAP, your organisation's Exchange server or Microsoft 365. Your mail is kept on your computer, so it opens instantly and stays readable offline.

Try it in your browser Download

The browser version opens a sample mailbox: nothing to install, nothing sent anywhere. Free and open source, MIT or Apache-2.0.

Quatrelle with the sample mailbox: the folder pane with Favorites and unread counts, the ribbon with Reply, Quick steps, Flag, Categorize, Pin and Snooze, the Inbox grouped under Today, Yesterday, Monday and Last week, and a flagged message open in the reading pane

One email client for IMAP, JMAP, Exchange and Microsoft 365

Any IMAP or POP provider: With SMTP to send; settings found from your address, SSL/TLS or STARTTLS, Gmail and Outlook.com included.
Exchange on-premises: Your organisation's own Exchange server through EWS, found with Autodiscover: mail, calendars, contacts, shared mailboxes, public folders and the server's rules.
Exchange Online and Microsoft 365: Through Microsoft Graph, with sign-in in your browser (OAuth 2.0).
JMAP, CalDAV and CardDAV: Modern mail servers, plus calendars and address books kept in sync. Outlook data files (.pst) open too.

A familiar email client, kept on your computer

Dark mode with a search for storyboard across all folders: both messages of the conversation found and the reply open

Search every folder, even offline

Every folder is cached on disk, so search answers at once, with or without a connection. Narrow it down with from:, subject:, has:attachment or is:unread. Conversations, and a dark mode.

Writing a reply in the reading pane: the Message, Insert, Options, Format Text and Review tabs, the From, To and Subject fields, the signature and the original message below

Write in place

Reply, Reply all and Forward in the reading pane or in a window of their own. Formatting, pictures, attachments, signatures, Cc and Bcc, drafts saved to the server and an Outbox for mail written offline. S/MIME signing and encryption.

The calendar's week view: the date navigator on the left, the ribbon with Day, Work week, Week and Month, and a week of appointments in their calendars' colours

Calendar, people and tasks

Day, week and month views, recurring events and time zones, meeting invitations you can accept or decline, the Scheduling Assistant and the Room Finder — on Exchange, CalDAV or this computer. An address book beside it.

The classic layout: the message list as a table with From, Subject, Received, Size and Categories columns, the reading pane at the bottom and the To-Do bar on the right

The layout you are used to

Three panes or the classic table, the reading pane on the right, at the bottom or off, and the To-Do bar. The everyday shortcuts work as you expect:

Ctrl+N new, Ctrl+R reply, Ctrl+Shift+R reply all, Ctrl+F forward
Insert to flag, Delete, Backspace to archive, F9 to send and receive
Ctrl+E to search, Ctrl+Z to undo

Private by design

Your mail stays with you

No cloud relay: Quatrelle talks to your own mail servers directly over TLS, and keeps the mail on your computer.

Passwords in the system keychain

Windows Credential Manager, the macOS Keychain or the Secret Service, never Quatrelle's own files.

No trackers in your mail

HTML mail is shown as formatted text; pictures from the web load only when you ask.

Open and clean-room

Built in Rust from the public standards (the RFCs) and Outlook's visible behaviour. MIT or Apache-2.0.

Why “Quatrelle”?

A quatrelle is a Renault 4L — the yellow van the postman drove from one mailbox to the next, never in a hurry and never leaving a letter behind. Ours is a little rusty in places, and that is the point: Rust is the language underneath.

Download Quatrelle for Linux, Windows or macOS

Linux	AppImage, `.deb`, `.rpm`, Flatpak and `.tar.gz` (x86_64, aarch64, riscv64)
Windows	`.msi` installer and a portable zip (x64, x86, ARM64)
macOS	`.dmg` (universal)
FreeBSD	tarball

Get the latest release Source code on GitHub

The Windows and macOS installers aren't signed yet: Windows SmartScreen asks you to confirm (More info, then Run anyway), and macOS to allow the app in System Settings, Privacy & Security.