Mailspring

Mailspring is an open-source desktop app that provides a desktop interface for managing email accounts. It is designed to reduce CPU and RAM usage to improve battery life on laptops. The application is available for Windows, macOS, and Linux via deb, rpm, and snap packages, making it accessible across the most common desktop operating systems.

The software operates as a local client that connects to email providers using IMAP. It handles synchronization through a local engine, ensuring that email credentials remain on the user's machine rather than being sent to a cloud server. Users can install the application via compiled binaries or run it from source using npm, which allows developers to modify the core logic or test new features in a local environment.

Key features

• Unified Inbox for managing multiple accounts in one view
• Snooze and Send Later functionality for scheduling emails
• Custom Mail Rules for automating inbox organization
• Email Templates for frequent responses
• Local C++ sync engine based on Mailcore2
• Plugin architecture for extending application functionality
• CSS based themes for interface customization
• Support for localization and community translations

The application is built using Electron, React, and TypeScript for the user interface, while the sync engine is written in C and C++. This hybrid architecture allows the software to maintain a modern web-based UI while utilizing a high-performance backend for data synchronization. This design makes the app particularly suitable for developers who wish to extend the software by building custom plugins or themes. While the core UI and sync engine are licensed under GPLv3, the software also offers a Pro subscription that adds link tracking, read receipts, and mailbox analytics for high-volume senders.

Mailspring is a customizable, resource-efficient email client for users who prefer a local sync engine over cloud-based alternatives.