Open Source Microsoft Outlook Alternatives
A curated collection of the 2 best open source alternatives to Microsoft Outlook.
The best open source alternative to Microsoft Outlook is Tuta. If that doesn't suit you, we've compiled a ranked list of other open source Microsoft Outlook alternatives to help you find a suitable replacement. Other interesting open source alternative to Microsoft Outlook is Twake Mail.
Microsoft Outlook alternatives are mainly Email & Communication but may also be Data Security & Privacy. Browse these if you want a narrower list of alternatives or looking for a specific functionality of Microsoft Outlook.
An email service with end-to-end encryption built in, with open source clients for mobile, desktop and the browser for privacy-conscious users.
End-to-end encryption in Tuta Mail is built in rather than bolted on, so the secure email service lets you communicate with anyone across every device you use. This repository holds the client source, which means the code handling your messages can be read and compiled by anyone who wants to check what it does.
Clients cover the places people actually read mail. Android builds are distributed through Google Play and through F-Droid for anyone avoiding proprietary stores, and there is an iOS app, a desktop client and a browser client. Building a client and developing on the codebase are documented as separate tasks, each with its own guide.
The project runs on a few clearly stated conventions.
- Building: a dedicated document covers compiling the clients from this repository.
- Developing: a hacking guide describes the workflow for anyone changing the code.
- Translating: a translation guide explains how to contribute a new language.
- Feature requests: these go through Reddit or support mail rather than the issue tracker.
- No generated contributions: issues and comments produced with help from large language models are closed or deleted without further explanation.
That last rule is unusually explicit, and maintainers say they prefer an incomplete or machine-translated report to an AI-assisted one. A public roadmap shows what the team plans next, and the community forum sits on Reddit. Anyone weighing up the service can read the roadmap and the client code together, since what a mail client really does is visible here.
Multi-platform email client built on the JMAP protocol, for organizations running Twake Mail or any other JMAP server.
Twake Mail is an email client from Linagora that speaks JMAP rather than IMAP, written in Flutter so one codebase covers phones, tablets and the web. It removes the need to maintain a separate native client per platform, and the need to accept whatever client a mail provider ships.
The argument for the switch is that IMAP was designed in another age and grew into a chatty patchwork of extensions, heavy on bandwidth and round trips, which is why large providers wrote proprietary protocols instead. JMAP answers that with HTTP and JSON, and Linagora maintains a Dart JMAP client for anyone writing their own application.
What ships today is a straightforward client for reading, sending and searching mail.
- Mobile apps: Android and iOS builds are published by Linagora on both app stores.
- Large screens: tablets and wide layouts were handled early rather than stretched to fit later.
- Web client: an early web build ships as a Docker image and reads the server address from an environment file.
- Server choice: the client works against any JMAP server, not only the Twake Mail backend.
- Branding: documentation covers changing logos and customizing the application grid.
A Docker Compose file brings the web client up alongside a test backend with demo accounts, and translations come through Weblate. Richer filters, labels, delegated access, restoring deleted messages and a GPG encrypted mailbox are described as work in progress rather than finished. Calendar and contacts extensions are out of scope, being neither standardized as RFCs nor implemented on the backend.
