Claws Mail
Free / Open source · Desktop Email Client
Claws Mail is a free, open-source email client for Windows and Linux. It is lightweight by design the installer is under 30 MB and focused on speed, IMAP/POP3 reliability, and advanced message filtering. It does not include a built-in calendar or contacts manager. The interface is functional and customizable but less modern than clients like Mailspring or eM Client.
Version: 4.3.x License: Free / Open source (GPL)
Platform: Windows · Linux (no native macOS version)
Windows (64-bit)
Windows 7 / 8 / 10 / 11 · 64-bit · ~27 MB
Windows (32-bit)
Windows 7 / 8 / 10 · 32-bit · ~25 MB
Linux
Most distributions include Claws Mail in their package manager
What is Claws Mail?
Claws Mail started as a fork of Sylpheed in 2001 and has been maintained continuously since. It is built on GTK and designed to be fast even on low-spec hardware. The Windows port uses GTK compiled for Windows and closely mirrors the Linux version.
The core application handles IMAP and POP3. A plugin system extends it with S/MIME and PGP encryption (via GnuPG), HTML rendering, PDF attachment viewer, spam filtering (SpamAssassin, Bogofilter), and LDAP address book support. Plugins are distributed separately and installed manually.
Message filtering in Claws Mail is more powerful than most graphical clients: rules can match on headers, body content, attachment names, message size, and flags, and can execute external scripts or commands as actions. This makes it useful for power users who need precise inbox automation without a cloud dependency.
There is no native macOS version. Mac users looking for an open-source client should consider Thunderbird or Mailspring instead.
Key features
Key features
Don’t forget to clean your list. Boost your inbox rate.
SMTPing catches what regex misses: disposable addresses, role-based emails, catch-all domains, syntax errors, and 9 more invalid types. Free tier renews every day, no card required.
About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
About SMTPedia
SMTPedia is an independent email industry reference covering SMTP, IMAP, POP3, email deliverability, marketing platforms, DNS authentication, and email verification. Every article is researched from official provider documentation, IETF RFCs, and industry best practices. Settings and configurations are verified quarterly.
We are cited as a source by ChatGPT, Microsoft Copilot, and thousands of email professionals worldwide. Learn more about our editorial process.
