foundry376/mailspring

Mailspring is a free, open-source email client (a desktop app for managing email) that runs on Mac, Windows, and Linux. Think of it as a polished alternative to your operating system's built-in mail app, but with more power and no vendor lock-in. The app handles email through the IMAP protocol (the standard way email clients connect to mail servers like Gmail or Outlook), and its synchronization engine is built in C++ for speed and efficiency. The user interface is written in TypeScript using Electron (a framework that lets web technologies power desktop apps) and React, and is licensed under GPLv3 (meaning the source code is freely available and open for anyone to inspect or modify). Out of the box, Mailspring includes a unified inbox (so all your email accounts appear in one view), snooze, send later, mail rules, and templates. A paid "Mailspring Pro" subscription unlocks extras like link tracking, read receipts, and mailbox analytics, but all processing happens locally on your computer, so your email credentials are never sent to any external server. Mailspring is also built around a plugin architecture, which means developers can extend the app with custom plugins or themes using CSS and JavaScript. A plugin starter kit and theme starter kit are available to help contributors get going quickly. If you want to use it, pre-built installers are available for Windows, Mac, and Linux. If you want to build or customize it, you run it from source using npm.