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Claws Mail vs Becky! Internet Mail: catalog facts
Claws Mail	Becky! Internet Mail
Free Free and open source under the GPL 3.0 or later.	Paid Shareware that requires a paid licence after evaluation.
Windows, macOS, Linux	Windows
Opens and searches enormous mail folders without stalling Plugins for PGP, spam filtering, RSS and calendars ship with it	Small, fast native Windows program Multiple mailboxes with separate profiles
Composes plain text by default; HTML mail sending is deliberately limited The interface is functional and looks like it was designed in 2004	Windows only HTML mail relies on an Internet Explorer component
Downloadable app	Downloadable app
Open source	Closed source
License: GPL-3.0-or-later	License not stated
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.