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Tuta Desktop vs Proton Calendar: catalog facts
Tuta Desktop	Proton Calendar
Freemium A free account with limited storage and one address. Paid plans add custom domains…	Freemium Free account available, with paid Proton plans and a business version.
Windows, macOS, Linux	Android, iOS, Web
End-to-end encrypts mail bodies, subject lines, calendar and contacts Password-protected messages to recipients who are not Tuta users	End-to-end encryption of event details Built-in scheduling for booking meetings
No IMAP or SMTP, so third-party mail clients cannot be used A Tuta account is required; it is not a general mail client	Requires a Proton account Works best within the Proton ecosystem
Downloadable app	Downloadable app, Web application, Hosted service
Open source	Closed source
License: GPL-3.0	License not stated
Account needed	Account needed
Needs internet	Not stated if it works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked September 23, 2026

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