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Aerion vs Claws Mail: catalog facts
Aerion	Claws Mail
Free Free and open source under the Apache 2.0 licence.	Free Free and open source under the GPL 3.0 or later.
Windows, macOS, Linux	Windows, macOS, Linux
Built with Wails instead of Electron for lower resource use Direct IMAP and SMTP connection with mail stored locally	Opens and searches enormous mail folders without stalling Plugins for PGP, spam filtering, RSS and calendars ship with it
Young project with a smaller feature set than established clients Tracking protection is described as basic	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
Open source	Open source
License: Apache-2.0	License: GPL-3.0-or-later
No account needed	No account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked October 1, 2026	Official website Full listing and sources Checked September 21, 2026

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