Kontact is a personal information manager and groupware software suite developed by KDE. It supports calendars, contacts, notes, to-do lists, news, and email. Developed by KDE
License: Open Source
Postbox offers a robust, user-friendly email management experience with advanced organization tools, but it comes at a cost. Kontact, being open-source, provides extensive integration and customization options, particularly for users within the KDE ecosystem, but may present a steeper learning curve.