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

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