The best open source alternative to Apple Mail is Thunderbird. If that doesn't suit you, our users have ranked more than 100 alternatives to Apple Mail and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Apple Mail are Proton Mail, Tuta Mail, K-9 Mail and Betterbird.
Cross-platform email client supporting multiple identities, chat, and strong filtering. Extend functionality with add-ons like RSS/Atom feed readers and PGP support.
Proton Mail provides secure email services with end-to-end encryption, ensuring data protection. Swiss-based and outside US jurisdiction, it offers a free version to champion privacy as a human right. Fully accessible on any device.
Offers comprehensive encryption for email, calendar, and contacts with zero personal info required. Built on open source, install via Play Store, F-Droid, or APK, with Tor and VPN support. Both free and paid plans; utilizes quantum-resistant encryption ensuring privacy-focused, anonymous usage.
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.
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.
Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.
Open-source, privacy-focused email client offering features such as encryption via OpenPGP and S/MIME, unlimited accounts, a unified inbox, customizable settings, and reformatted emails to prevent phishing. Supports two-way synchronization and provides Pro features for additional customization.
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. 4GB cost 1€/month. Information is hosted on encrypted hard drives. Electricity from renewable resources is used.
Geary is an email application built around conversations, for the GNOME 3 desktop.
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.
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.
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It has too crowded a look to listing email. Compare the wide screen view of both. Thunderbird puts all the details on one line, apple uses multiple lines and gives whitespace between mails.