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Proton Mail vs Posteo: catalog facts
Proton Mail	Posteo
Freemium Free accounts work in the mobile and web apps; the desktop apps are offered as a free…	Paid 1 euro per month, with paid upgrades for storage and aliases.
Windows, macOS, Linux, Android, iOS, Web	Web
End-to-end encrypted email by default Apps for iOS, Android, macOS, Windows, Linux and the web	Signup without personal details Low fixed monthly price
Only works with a Proton account Desktop apps need a paid plan after the trial	No free tier 4 GB base storage
Downloadable app, Web application, Hosted service	Web application, Hosted service
Closed source	Closed source
License not stated	License not stated
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 September 23, 2026

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