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Proton Calendar vs Fastmail: catalog facts
Proton Calendar	Fastmail
Freemium Free account available, with paid Proton plans and a business version.	Paid Paid subscription with a 30-day free trial that needs no credit card.
Android, iOS, Web	Android, iOS, Web
End-to-end encryption of event details Built-in scheduling for booking meetings	Email, calendar and contacts in one service Choice of EU or USA data residency
Requires a Proton account Works best within the Proton ecosystem	No free plan after the trial Hosted service, so your mail lives on Fastmail's servers
Downloadable app, Web application, Hosted service	Downloadable app, 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.