mailspring

Mailspring is a desktop email application for macOS, Windows, and Linux, descended from Nylas Mail. Its user interface is open source under GPLv3 and built with TypeScript, Electron, and React. The mail sync engine is a separate GPLv3 C++/C component based on Mailcore2; it runs locally on the user's computer, and development environments can use prebuilt engine binaries instead of compiling them. The client includes a unified inbox, snooze, send later, mail rules, templates, and a revised composer. An optional Mailspring Pro subscription adds link tracking, read receipts, mailbox analytics, and contact and company profiles. The project states that these features run in the client and that email credentials are not sent to its cloud. Mailspring is designed for extension through a plugin architecture and CSS-based themes. Starter repositories are provided for plugins and themes, and the project documentation covers local development, testing, builds, localization, and contribution workflows. The application can be run from source with npm install and npm start, and built using npm run-script build. Prebuilt downloads are provided for Windows, macOS, and Linux in deb, rpm, and snap formats where applicable.