14 open-source email clients
Open Source Email Clients for Desktop
The most popular open-source email clients for Windows, macOS and Linux on GitHub are Folo, Mailspring and NetNewsWire. appsgit lists 14, including free alternatives to Microsoft Outlook, each with its platforms, license and install commands.
Updated Oct 8, 2026
Open Source Email Clients for Desktop
Folo
RSSNext/Folo
Folo is an open-source AI RSS reader that brings everything you follow into one calm timeline, then helps you read it.
Email & calendarWindowsmacOSLinuxMailspring
Foundry376/Mailspring
A beautiful, fast and fully open source mail client for Mac, Windows and Linux.
Email & calendarWindowsmacOSLinuxNetNewsWire
Ranchero-Software/NetNewsWire
NetNewsWire is a free and open-source feed reader for macOS and iOS.
Email & calendarmacOSFluent Reader
yang991178/fluent-reader
Modern desktop RSS reader built with Electron, React, and Fluent UI.
Email & calendarWindowsmacOSLinuxMeetingBar
leits/MeetingBar
🇺🇦 Your meetings at your fingertips in the macOS menu bar.
Email & calendarmacOSRssguard
martinrotter/rssguard
Feed reader (podcast player, basic XMPP client and also Gemini protocol client) which supports RSS/ATOM/JSON and many web-based feed services.
Email & calendarWindowsmacOSLinuxVienna RSS
ViennaRSS/vienna-rss
Vienna is a free and open-source RSS/Atom/JSON feed newsreader for macOS.
OfficialEmail & calendarmacOSLettura
zhanglun/lettura
Lettura Follow your favorite content and never miss a story.
Email & calendarWindowsmacOSLinuxWino Mail
bkaankose/Wino-Mail
Built-in Mail & Calendars app clone for Windows.
Email & calendarWindowsLunarBar
LunarBar-app/LunarBar
A compact lunar calendar for your macOS menu bar.
Email & calendarmacOSMail
flectar/mail
Built from the ground up for speed. Flectar Mail delivers native performance, instant startup, and as little as 20 MB of RAM.
OfficialEmail & calendarWindowsmacOSLinuxFeed Flow
prof18/feed-flow
FeedFlow is a minimalistic RSS Reader available on Android, iOS, macOS, Windows and Linux.
Email & calendarWindowsmacOSLinuxPapr
l0ng-ai/papr
A fast, native RSS reader — plus an agent-facing CLI so your AI agent can read, search and triage your feeds from the shell.
Email & calendarWindowsmacOSLinuxThunderbird
thunderbird/thunderbird-desktop
The official repository for the Thunderbird desktop email client.
OfficialEmail & calendarWindowsmacOSLinux
What are the best open-source email clients?
By GitHub stars, Folo is the most popular (39,072 stars), followed by Mailspring and NetNewsWire. People often use these instead of Microsoft Outlook. Each page lists the platforms, license and last commit.
Which of these run on Windows, Mac and Linux?
10 of the 14 open-source email clients listed here run on Windows, 13 on macOS and 9 on Linux; on a Mac, the most starred is Folo. 6 can be installed with a package manager such as Flathub, Homebrew, winget or Chocolatey.
Are these open-source email clients free?
Yes. All 14 use an open-source license (OSI-approved or FSF-free), so you can use, copy and change them for free.
How are these open-source email clients chosen?
Apps come from desktop awesome lists (Awesome Linux Software, awesome-mac, awesome-windows, awesome-electron and the media and file sections of awesome-cli-apps), more than 70 GitHub topics such as desktop-app, electron-app, tauri-app, gtk, qt, macos-app, pdf-editor, cad and remote-desktop, and a hand-picked list of flagship apps. An app is listed only if it has a license (one GitHub detects, or one appsgit checked by hand), a README and a commit in the last six months, is not archived or a fork, and has 1000+ GitHub stars (topics), 500+ (awesome lists) or 100+ (hand-picked). It must also be an end-user application with a desktop signal: installers in its releases, install instructions for Windows, macOS or Linux, or a Flathub, Homebrew, winget, Chocolatey, Snap or AUR package. Libraries, frameworks, themes, plugins and servers are left out, and source-available apps are labelled as such.