Open-source Mailbird alternatives

Mailspring is a desktop email client for Mac, Windows and Linux, built as a new version of Nylas Mail by one of its original authors. The interface is written in TypeScript with Electron and React, and the mail sync engine is written in C++ and runs locally on your computer. Both parts are open source under GPLv3.

Features include a unified inbox, snooze, send later, mail rules and templates, and a plugin architecture makes the app easy to extend. The README states that these features run in the client and that email credentials are not sent to the cloud. The IMAP-based sync engine replaces the earlier JavaScript sync code used by Nylas Mail.

A paid Mailspring Pro subscription unlocks extra features for people who send a lot of email, such as link tracking, read receipts, mailbox analytics and contact and company profiles. Compiled downloads are offered for Windows, macOS and Linux, including deb, rpm and snap packages.

Zero is an open-source email application presented as a Gmail alternative that applies AI to the inbox. Its authors argue that most email services are closed source, data-hungry or too complex to host yourself, and they position Zero as transparent and privacy-first. It can be self-hosted while also connecting to external services such as Gmail and other email providers.

Listed strengths include a unified inbox that combines multiple providers such as Gmail and Outlook, AI agents and language models that help with email tasks, a customizable interface and an extensible design for developers. The project states that it does not track, collect or sell your data, while noting that data passed to connected external services falls under those services' own privacy terms.

The stack is Next.js, React, TypeScript, Tailwind CSS and shadcn UI on the front end, Node.js with Drizzle ORM on the back end, PostgreSQL for the database, and Better Auth with Google OAuth for sign-in. Running it locally requires recent Node.js, pnpm and Docker, plus environment variable configuration. The code is MIT licensed and the latest release listed is v0.1.

This repository is an experimental copy of Mozilla's comm-central tree, set up so it can be forked on GitHub. Its README is the Thunderbird project README: Thunderbird is an open-source, customizable email client built on the same Mozilla platform that Firefox uses.

To build Thunderbird you need the Firefox repository as well, because the Thunderbird code lives in a comm subdirectory inside the Firefox source tree and the two share a lot of platform code. The README points to a Getting Started guide, a Building Thunderbird guide, a developer website and rendered source tree documentation.

Contributors can join the project's mailing lists, including a moderated planning list for higher-level topics such as future features, and follow the contributing pages on the Thunderbird site. The code is mostly JavaScript, and this repository holds the source rather than the packaged email application.

Mailpile is a modern web-mail client that aims to make private email easier, with user-friendly encryption and an emphasis on a clean interface. It was designed to make receiving and sending PGP-encrypted or signed email convenient, and its development was funded by a large community of backers.

Its core is a custom-written search engine built to handle large volumes of email on consumer hardware. Mail is organized with tags, similar to Gmail labels, and incoming messages can be tagged automatically through static rules or Bayesian classifiers. The primary interface is web-based, with a basic command-line interface and an API for developers, so it can run as a local desktop application or as web-mail on a personal server.

The README now carries a notice that development on this codebase has halted until the Python 3 rewrite is complete, and it points to legacy Docker images for anyone who needs to open version 1 data. The repository metadata lists the license as Other, while the project says its code is released under an OSI-approved free software license.