Claws Mail
Claws Mail is a free and open-source email client and newsreader designed for lightweight, fast performance and user-friendly operation, primarily built on the GTK+ graphical toolkit.[1][2] Originally developed in April 2001 as Sylpheed-Claws, a testing branch of the Sylpheed email client to experiment with new features, it evolved into an independent project and was renamed Claws Mail in November 2006.[3][4] The software supports multiple protocols including POP3, IMAP, SMTP (with authentication), NNTP for news, and LDAP for address book integration, along with features such as multiple account management, message threading, filtering, and encryption via plugins.[5][2] It is distributed under the GNU General Public License (GPL) and uses the MH message storage format for efficient handling of large mailboxes.[1] Claws Mail runs on Unix-like operating systems such as Linux, BSD, and Solaris, as well as Windows, with ports available for macOS, emphasizing quick response times, extensibility through plugins (e.g., for RSS aggregation and calendar integration), and a sophisticated yet intuitive interface.[6][7][8] As of February 2025, the project remains actively maintained, with the latest stable release being version 4.3.1.[9]Introduction
Overview
Claws Mail is a free and open-source email client and news reader built on the GTK+ graphical user interface toolkit.[2][10] It serves as a versatile tool for managing email and Usenet news, prioritizing user-friendly functionality for both novice and advanced users across diverse computing environments.[10] The software emphasizes a lightweight design that delivers quick response times and minimal resource consumption, rendering it ideal for Unix-like operating systems, Windows, and hardware with limited capabilities.[10][11] This approach ensures efficient performance without compromising on essential features, allowing seamless operation even on resource-constrained systems.[2] At its core, Claws Mail incorporates design principles focused on intuitive usability, extensibility via plugins, and the adoption of the MH format for local email storage to enable secure, rapid data handling.[10] Originating in 2001, it evolved from prior email clients to strike a balance between straightforward operation and customizable options, promoting stability and robustness in everyday use.[10]Licensing and Platforms
Claws Mail is released under the GNU General Public License (GPL) version 3 or later, a copyleft license that guarantees users the freedom to run, study, share, and modify the software, while requiring any derivative works to be distributed under the same terms. This licensing model promotes open-source collaboration and ensures the source code remains freely available for inspection and adaptation. The software is primarily designed for Unix-like operating systems, including Linux distributions and BSD variants, where it integrates seamlessly with the GTK+ graphical toolkit. Ports enable compatibility with Microsoft Windows, providing native installers for stable operation on that platform. Support for macOS exists on an experimental basis, typically achieved through third-party package managers such as MacPorts or Homebrew, though official binaries are not provided. Claws Mail does not offer native versions for mobile operating systems like Android or iOS.[12][13][7] With a focus on lightweight design, Claws Mail maintains a minimal system footprint, requiring GTK+ 3.x or later for its graphical interface in current releases (version 4.x series). It supports both 32-bit and 64-bit architectures, allowing deployment on a wide range of hardware from older systems to modern processors without demanding excessive resources.[14][15] Distribution occurs through multiple channels to accommodate diverse user environments: binary installers and source tarballs are available directly from the official website, facilitating easy downloads for Windows users and developers. On Linux and BSD systems, it is packaged for repository managers, such as apt in Debian-based distributions and dnf (successor to yum) in Fedora-based ones, enabling straightforward installation via system updates. Users can also compile from source for custom builds, ensuring flexibility across supported platforms.[16][17]User Interface and Core Functionality
Main Interface Components
Claws Mail employs a classic three-pane layout to facilitate efficient email management, consisting of a folder list on the left, a message list in the center, and a message view on the right.[18] This design allows users to navigate folders, select messages, and preview content seamlessly within a single window.[18] Users can toggle the message view pane on or off using the 'v' key, effectively switching to a two-pane mode for a more compact interface when focusing solely on message lists, which expands the center pane accordingly.[18] To enhance accessibility for power users, Claws Mail provides extensive keyboard shortcuts for core operations, enabling rapid navigation, composition, and searching without relying on the mouse.[18] For instance, 'n' and 'p' keys move to the next and previous messages, respectively, while 'Shift+n' jumps to the next unread message; composing a new email is initiated with 'Ctrl+m', and sending uses 'Ctrl+Return'.[18] Search functions are similarly shortcut-driven, with '/' focusing the quick search bar and 'Shift+Ctrl+f' opening a dedicated folder search dialog.[18] These shortcuts promote usability across diverse workflows, from casual browsing to intensive email handling. The interface supports customization of toolbars and menus to adapt to user preferences and display constraints, including the selection of icon themes for visual consistency.[18] Access to these options is available through the Configuration > Preferences > Toolbars menu, where users can add, remove, or rearrange buttons and incorporate custom icons from available themes hosted on the official site.[18] Layout adjustments, such as resizing panes or hiding elements, further ensure compatibility with various screen sizes, maintaining readability on both small laptops and large monitors.[18] Integrated search and filtering tools are prominently embedded in the interface to streamline message retrieval, with quick folder search accessible via a magnifying glass icon in the toolbar for recursive scanning of subfolders.[18] For broader queries, the global message indexing feature, invoked through the Extended Quick Search dialog, allows searching across all accounts using criteria like sender, subject, or date, delivering results in a dedicated list view.[18] These tools emphasize accessibility by providing both simple, icon-based entry points and advanced options, reducing the time needed to locate specific emails amid large inboxes.[18]Account and Message Management
Claws Mail supports the configuration of multiple email accounts, allowing users to manage unlimited profiles simultaneously for seamless integration of personal and professional correspondence. It accommodates standard protocols including POP3 for retrieving messages from remote servers, IMAP4 for synchronized access across devices, and SMTP for outgoing mail transmission. Authentication mechanisms such as APOP for POP3 and various options for SMTP ensure secure connections, while SSL/TLS encryption is available per account to protect data in transit against interception.[19][18] Locally, messages from POP3 and local mbox accounts are stored in the MH format, which organizes emails as individual files within folders to facilitate rapid indexing and retrieval without loading entire archives into memory. This structure enables efficient offline access to cached content, supporting operations like searching and sorting even without an internet connection. For interoperability, Claws Mail provides import and export capabilities in mbox format, ensuring compatibility with other clients such as Thunderbird through standard file-based migrations.[19][18] Organization of messages is enhanced through threading, which groups related emails by subject or specific headers like In-Reply-To, with configurable settings such as a default 10-day maximum thread age to maintain relevance. Users can apply color labels or tags to categorize messages visually, aiding in quick identification and prioritization. Filtering rules further streamline management by evaluating headers—including sender, recipient, subject, and custom fields—to apply actions like automatic sorting into designated folders upon receipt.[19][18] The client handles attachments and complex message structures robustly, parsing multipart MIME types to display inline images directly within the message view while separating discrete files for download. This includes support for embedded content in HTML emails, with options to save multiple attachments collectively or individually. Integration hooks for virus scanning are provided via the Clamd plugin, which leverages ClamAV to inspect incoming messages and attachments for malware during processing.[19][18]Advanced Features and Extensibility
Plugin System
Claws Mail employs a plugin system that enables dynamic loading of extensions through shared libraries with a ".so" suffix, installed in the directory$PREFIX/lib/claws-mail/plugins/.[20] These plugins integrate seamlessly into the core application without modifying its source code, allowing users to extend functionality such as filtering, notifications, and rendering capabilities.[21] Plugins are loaded manually via the in-app "Configuration > Plugins" menu, where users can select and activate them, or automatically if dependencies are met during installation.[20]
As of February 2025, 31 official plugins are available, distributed as part of the Claws Mail source package and downloadable from the project's website, with many requiring external libraries like GnuPG for cryptographic features.[21] Core plugin categories include notifications for alerting users to new mail, such as the Notification plugin which acts as a mail notification daemon, RSS/Atom feed reading via the RSSyl plugin, and address book enhancements through the AddressKeeper plugin.[21]
Installation of plugins can occur automatically using the built-in plugin manager within Claws Mail, which handles loading and dependency checks, or manually by compiling from source after downloading the plugin modules.[20] This approach ensures that plugins enhance the user interface and core operations, such as message viewing and account handling, while maintaining the application's lightweight design.[21]
Representative examples of official plugins illustrate the system's versatility: the Fancy plugin provides advanced HTML rendering for emails, the PGP/Inline plugin enables inline PGP encryption and decryption for secure messaging, and the PDF Viewer plugin supports handling PDF attachments directly within the client.[21]