Open Source Email Clients

Cross-platform email client providing POP/IMAP support, robust filtering, multiple accounts, and chat. Extendable via add-ons with RSS/Atom, etc.

Secure Swiss-based email with end-to-end encryption and zero third-party access. Available across devices, offering a free version to promote privacy.

End-to-end encrypted app for email, calendar, and contacts, requiring no personal data, with open source code and quantum-resistant security.

K-9 is an open source email client for Android with multi-folder sync, email signatures, Bcc-to-self, return-address configuration, keyboard shortcuts, Exchange Support, message flagging, IMAP deletes, saving attachments, configurable notifications and more.

Open-source client enhancing Thunderbird with more features and bug fixes. Offers security patches and multi-row descriptions like Outlook.

Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.

Web-browser, advanced e-mail, newsgroup and feed client, IRC chat, and HTML editing in one application. Itis built on the open source Mozilla Gecko engine, the same code which underlies Thunderbird and is the base for the Firefox browser.

Privacy-focused, open-source email app offering encryption, unlimited accounts, customizable features, unified inbox, and low data usage.

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.

Web- and IMAP-based email service. 2GB cost 1€/month. Information is hosted on encrypted hard drives. Electricity from renewable resources is used.

Roundcube webmail is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an e-mail client, including MIME support, address book, folder manipulation, message searching and spell checking.

GTK+-based client offering fast performance, news reading, robust stability, extensibility via plugins, advanced filtering, encryption, folder and contact management.

Geary is an email application built around conversations, for the GNOME 3 desktop.

Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features. The development of Mailpile is funded by a large community of backers and all code related to the project is and will be released under an OSI approved Free Software license.

Privacy-friendly Swiss email solution with 20 GB free storage, custom domain options, contact and calendar sync, and cross-device access in a secure suite.

Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).

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...

ElectronMail is an Electron-based unofficial desktop client for ProtonMail and Tutanota end-to-end encrypted email providers. The app aims to provide enhanced desktop user experience enabling features that are not supported by the official in-browser web clients.

App to sync encrypted emails from Proton Mail with desktop email clients such as Mozilla Thunderbird, Apple Mail, and Microsoft Outlook.

Personal Information Manager (Mail, Contact, Calendar and more).

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.

Kolab provides a FOSS communication & collaboration solution that can be completely self-hosted. Take back control of your data and access it via the webinterface, or existing mobile & desktop clients.

Nylas Mail was superseeded largely by two forks - Mailspring and Nylas Mail Lives.

KMail is the email component of Kontact, the integrated personal information manager of KDE. Kontact is a personal information manager and groupware software suite for KDE. It supports calendars, contacts, notes, to-do lists, news, and email.

Simple, modern & fast web-based email client. Modest system requirements, decent performance, simple installation and upgrade, no database required. All these make RainLoop Webmail a perfect choice for your email solution.