Claws Mail Alternatives for Linux

Thunderbird is a free, open-source email client developed by the Mozilla Foundation, offering robust features for managing multiple email accounts, integrated chat, and RSS feeds. Known for its extensibility and focus on user privacy and security.

Evolution is a comprehensive personal information manager for the GNOME desktop environment, designed to manage emails, contacts, calendars, and tasks. It provides a unified interface for various communication and organizational needs.

Geary is a modern email client designed for the GNOME desktop, emphasizing a conversational view for streamlined email management. It offers a clean interface, supports multiple accounts, and integrates with the GNOME environment to provide a cohesive user experience for organizing and sending emails.

Sylpheed is a free and open-source email and news client known for its lightweight design and speed, focusing on usability and efficient handling of large email collections without burdening system resources.

Mutt is a highly configurable, text-based email client for Unix-like systems. It offers powerful features for advanced users who prefer a lightweight and efficient email management experience directly from the command line.

Zimbra Desktop provides a unified interface for managing multiple email accounts, calendars, tasks, and contacts offline. It supports various protocols like IMAP, POP, CalDAV, and CardDAV, offering a comprehensive personal information management solution.

OpenProject is a powerful, web-based open-source project management software designed for teams of all sizes. It offers comprehensive tools for managing projects, tasks, teams, and communication in one centralized platform. Ideal for organizations prioritizing collaboration, flexibility, and data control.

KMail is a powerful and flexible email client tightly integrated with the Kontact personal information manager suite. Part of the KDE ecosystem, it offers robust features for managing your email, including strong encryption options, support for multiple protocols like IMAP, POP3, and Exchange, and seamless integration with other Kontact components like the calendar and address book.

Open365 is a comprehensive, open-source productivity suite offering cloud storage, office applications, and communication tools. Built upon a foundation of open-source technologies like KDE, Seafile, and LibreOffice, it provides a robust alternative to proprietary solutions, emphasizing privacy and control.