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Proton Mail vs Aster Mail: catalog facts
Proton Mail	Aster Mail
Freemium Free accounts work in the mobile and web apps; the desktop apps are offered as a free…	Freemium Free plan with 10 GB of storage; paid plans start at $2.99 per month.
Windows, macOS, Linux, Android, iOS, Web	Android
End-to-end encrypted email by default Apps for iOS, Android, macOS, Windows, Linux and the web	Mail is encrypted on the device before it leaves 10 GB free with custom domain support
Only works with a Proton account Desktop apps need a paid plan after the trial	The app only works with astermail.org accounts Young project with a small user base compared with established providers
Downloadable app, Web application, Hosted service	Downloadable app, Hosted service
Closed source	Open source
License not stated	License: AGPL-3.0
Account needed	Account needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked October 2, 2026

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