**Mailspring is a new version of Nylas Mail maintained by one of the original authors. It's faster, leaner, and shipping today!** It replaces the JavaScript sync code in Nylas Mail with a new C++ sync engine based on [Mailcore2](https://github.com/MailCore/mailcore2). It uses roughly half the RAM and CPU of Nylas Mail and idles with almost zero "CPU Wakes", which translates to great battery life. It also has an entirely revamped composer and other great new features.
Mailspring's UI is open source (GPLv3) and written in JavaScript with [Electron](https://github.com/atom/electron) and [React](https://facebook.github.io/react/) - it's built on a plugin architecture and was designed to be easy to extend. Check out [CONTRIBUTING.md](https://github.com/Foundry376/Mailspring/blob/master/CONTRIBUTING.md) to get started!
Mailspring's sync engine is spawned by the Electron application and runs locally on your computer. It will be open-sourced in the future but is [currently closed source.](https://github.com/Foundry376/Mailspring/blob/master/ROADMAP.md#why-is-mailsync-closed-source) When you set up your development environment, Mailspring uses the latest version of the sync process we've shipped for your platform so you don't need to pull sources or install it's compile-time dependencies.
Mailspring comes packed with powerful features like Unified Inbox, Snooze, Send Later, Mail Rules, Templates and more. Mailspring Pro, which you can unlock with a monthly subscription, adds even more features for people who send a ton of email: link tracking, read receipts, mailbox analytics, contact and company profiles. **All of these features run in the client - Mailspring does not send your email credentials to the cloud.** For a full list of features, check out [getmailspring.com](https://getmailspring.com/).
You can download compiled versions of Mailspring for Windows, Mac OS X, and Linux (deb, rpm and snap) from [https://getmailspring.com/download](https://getmailspring.com/download).
Mailspring's UI is entirely open-source and pull requests and contributions are welcome! There are three ways to contribute: building a plugin, building a theme, and submitting pull requests to the project itself. When you're getting started, you may want to join our [public slack](https://join-mailspring-slack.herokuapp.com/) so you can ask questions and learn from other people doing development.
Plugins lie at the heart of Mailspring and give it its powerful features. Building your own plugins allows you to integrate the app with other tools, experiment with new workflows, and more. Follow the [Getting Started guide](https://Foundry376.github.io/Mailspring/) to write your first plugin in five minutes. To create your own theme, go to our [Theme Starter guide](https://github.com/Foundry376/Mailspring-Theme-Starter).
The Mailspring user interface is styled using CSS, which means it's easy to modify and extend. Mailspring comes stock with a few beautiful themes, and there are many more which have been built by community developers. To start creating a theme, [clone the theme starter](https://github.com/Foundry376/Mailspring-Theme-Starter)!
If you are updating an existing Nylas theme for Mailspring here is a [step by step tutorial](https://foundry376.zendesk.com/hc/en-us/articles/115001918391-How-do-I-update-an-N1-Nylas-Mail-theme-for-Mailspring-). Notice: as part of the update process you will probably need to [import mailspring base variables](https://github.com/Foundry376/Mailspring/issues/326#issuecomment-343757775).
Pull requests are always welcome - check out [CONTRIBUTING](https://github.com/Foundry376/Mailspring/blob/master/CONTRIBUTING.md) for more information about setting up the development environment, running tests locally, and submitting pull requests.
