KMail

KMail is an email client for the KDE Desktop Environment and a core component of the KDE Applications suite. It is designed to work with Kontact, the KDE personal information manager, but can also be used standalone. KMail stores and manages messages using the Akonadi data storage framework, which provides centralized handling of mail, contacts, calendars, and other data across KDE applications.

It supports multiple email accounts and standard mail protocols, including IMAP, POP3, and SMTP. Users can organize mail with folders and tags, create message filters, and perform advanced searches. The interface emphasizes keyboard efficiency and integrates with KDE's desktop themes and widgets.

For security, KMail supports encryption and digital signing via OpenPGP and S/MIME, through integration with GnuPG and related tools. Messages can be encrypted or signed during composition, with key management accessible from the application. Passwords and credentials can be stored in KWallet.

Storage and integration: KMail uses Akonadi to index and cache mail data for fast access and offline work. It integrates with Kontact for calendar and contact access, and supports offline synchronization and multi-folder views. It runs on KDE-supported Linux and UNIX-like systems and is released under an open-source license as part of KDE Applications.