Claws Mail is a lightweight e-mail and newsgroup client developed since 2001, written from scratch in C language based on GTK+. Initially the application was available only for Linux operating systems. It is characterized by great configuration possibilities, friendly and simple graphical interface, as well as support for plug-ins, which can extend the functionality of the application.

The most popular add-ons include an RSS feed reader, a powerful organizer, an HTML browser, anti-spam filters and smaller gadgets, such as interesting notifications or LED support in some laptops. Claws Mail supports POP3, SMTP, IMAP4 and NNTP protocols, supporting encrypted connections and GPG signatures. It has a built-in search engine, spell filtering and spell-checking mechanism, allows you to import the mail in popular formats, support multiple mail accounts, as well as templates and graphical themes.