There are many alternatives to Microsoft Outlook for Windows if you are looking for a replacement. The best open source Windows alternative is Thunderbird. If that doesn't suit you, our users have ranked more than 100 alternatives to Microsoft Outlook and many of them are open source and available for Windows so hopefully you can find a suitable replacement. Other interesting open source Windows alternatives to Microsoft Outlook are Betterbird, Mailspring, Pelton and Claws Mail.
Cross-platform email client supporting multiple identities, chat, and strong filtering. Extend functionality with add-ons like RSS/Atom feed readers and PGP support.
United States
Betterbird, a soft fork of Mozilla Thunderbird, improves user experience with advanced features, bug fixes, security patches, and multi-row descriptions similar to Outlook. Compatible with multiple platforms and can be used alongside Thunderbird, sharing the same profile.
Germany
EU
Boost your productivity and send better email with Mailspring, a beautiful, fast email client for Mac, Windows, and Linux. Mailspring is free to use and an optional pro version adds read receipts, send later, reminders and more.
United States
Free, open-source client for Windows, macOS, and Linux, offering local email storage and search online or offline, privacy-focused with no telemetry or third-party servers, IMAP and SMTP support, intuitive interface, and multiple account support.
GermanyEU
Email and news client on GTK+ foundation featuring quick performance, extensible plugins, secure protocols, advanced filtering, strong folder and contact management, lightweight design, powerful search, customizable interface, multi-language support, and encryption.
Modern open-source email client supporting unified inbox, IMAP/SMTP, Gmail and Outlook with OAuth2, conversation threading, rich text TipTap composing, CardDAV contact sync, tracking removal, dark mode, color themes, vim-style shortcuts, and a detachable window.
Hong Kong SAR China
Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).
Japan
Mutt is a small but very powerful text-based mail client for Unix operating systems. Some of its features are: color support, message threading, MIME support (including RFC2047 support for encoded headers), PGP/MIME (RFC2015), various features to support mailing lists, including...
United States
Wino is a lightweight native mail client for Windows 10/11. It is still in active development. Main motivation for this project is to replace Mail & Calendar for Windows with modern Windows design without using web technologies for speed.
Türkiye
Scribe is a small portable email client with an intergrated contact database and calendar. It supports all the major internet mail protocols and uses international standards where possible. Scribe doesn't required installing or uninstalled and can be used from a removable...
Japan
Trojitá, is a fast Qt IMAP e-mail client that respects open standards and facilitates modern technologies. Trojitá values vendor-neutrality that IMAP provides and is committed to be as interoperable as possible.
CzechiaEU
