Does Proton Calendar support CalDAV?

If you’ve picked Proton for your email, you probably want your calendar to play nicely with the rest of your setup too. Here’s the catch: Proton Calendar doesn’t support CalDAV, which is why Apple Calendar, Thunderbird, and Outlook can’t sync with it.

In this article, we’ll cover why that limitation exists, what Proton offers in its place, and which private calendar services do support CalDAV.

Why doesn’t Proton Calendar support CalDAV?

It comes down to how end-to-end encryption works.

Proton encrypts every event on your device before it ever reaches their servers – that’s the whole pitch. CalDAV, by contrast, was designed to read and edit calendar data directly on the server. Those two ideas can’t coexist: a server that’s blind to your events by design can’t service a protocol that needs to see them.

So the gap isn’t an oversight. It’s the architecture working as intended.

The Proton community has been requesting CalDAV for over a decade. As of 2026, the feature request on Proton’s UserVoice forum has thousands of votes and remains unimplemented, with users still actively commenting that it’s “wild to me that people have been asking for such a straightforward feature for 10+ years.”

What does this mean for you in practice?

Your calendar isn’t available via native CalDAV sync.

Apps like Apple Calendar, Thunderbird, and DAVx⁵ are CalDAV-compatible clients. None of them can connect to Proton Calendar via CalDAV.

You can’t get live, two-way calendar sync between Proton and your preferred third-party app.

If your workflow depends on seeing one calendar across multiple apps, this is a real limitation.

It’s especially relevant if you use an Android phone with DAVx⁵, or if you manage shared schedules across different platforms.

What does Proton offer instead?

Proton Calendar supports subscribing to external calendars via URL, but it’s view-only.

You can add an iCal link from another calendar into Proton. It’ll display those events alongside yours.

You can also share your own Proton calendar as a link that others can subscribe to.

But there are two key limitations.

Subscribed calendars are read-only. You can’t edit or delete events from them.

And according to Proton’s support documentation, external calendars refresh every 8–16 hours, not in real time.

URL subscription is genuinely useful for low-stakes cases – peeking at a colleague’s schedule, pulling in public holidays, watching a sports calendar. It just isn’t built for the job CalDAV does, which is keeping your own events in sync everywhere you actually edit them.

How do private calendar services compare?

Here’s how the three main private calendar services stack up on CalDAV and interoperability:

Feature	Proton Calendar	Tuta Calendar	Mailfence
CalDAV sync	No	No	Yes
Two-way sync with third-party apps	No	No	Yes
URL-based calendar subscription	Yes (view-only, 8–16 hr refresh)	ICS import	Yes
End-to-end encrypted calendar events	Yes	Yes	No

Each provider picks its priorities. Proton and Tuta lock everything down with end-to-end encryption and accept the interoperability cost that comes with it. Mailfence takes a different route, keeping CalDAV open.

Neither answer is wrong; the right one depends on whether you’d rather your events stay unreadable to the server or stay reachable from every app you actually use.

Which calendar services actually support CalDAV?

If CalDAV matters to your workflow, you’ve got real options. Here are the main ones worth knowing about.

Mailfence

Mailfence supports full CalDAV on the free plan with no restrictions.

It works natively with Apple Calendar, Thunderbird, Outlook, DAVx⁵ on Android, and eM Client. You get real-time, two-way sync across all of them. That interoperability is intentional. As Mailfence co-founder Patrick De Schutter put it in a 2019 interview: “It’s designed to be highly interoperable with client/mobile devices via standard protocols such as CalDAV, CardDAV, ActiveSync, and IMAP.”

Your data lives on a server protected by Belgian privacy law. That makes it a strong pick if you want CalDAV and privacy from the same service.

Mailfence also covers end-to-end encrypted email, contact sync via CardDAV, and digital signatures – all from one account.

Nextcloud

If you want full control, Nextcloud lets you self-host your own CalDAV server.

Nextcloud Calendar supports two-way CalDAV sync with Apple Calendar, Thunderbird, DAVx⁵, and Outlook (via CalDAV Synchronizer plugin).

The trade-off is setup and maintenance. You need your own server or a hosted Nextcloud instance, and misconfigured TLS or authentication can cause sync failures.

For technically confident users, it’s the most private option – your data never leaves your hardware.

iCloud

Apple’s iCloud Calendar uses CalDAV under the hood.

If you’re already in the Apple ecosystem, it just works – no manual server config needed. You can also connect iCloud to Android via DAVx⁵ using an app-specific password.

iCloud isn’t a privacy-first service, though. Apple has access to your calendar data, and you’re tied to its ecosystem.

Fastmail

Fastmail has CalDAV support and syncs with Apple Calendar, Thunderbird, DAVx⁵, and apps like Morgen and Fantastical.

Fastmail is one of the few CalDAV services that supports push sync on Apple devices – so your events update instantly.

Fastmail is based in Australia and isn’t free. Plans start at $5/month on annual billing. But if CalDAV reliability is your top priority, it’s a solid choice.

What about the calendar apps themselves?

CalDAV has two sides: the server (where your data lives) and the client (the app you interact with).

The services above are servers. The clients that connect to them include:

• Apple Calendar: built-in CalDAV support on macOS and iOS
• Mozilla Thunderbird: full CalDAV support on desktop
• DAVx⁵: the go-to CalDAV sync app for Android
• eM Client: CalDAV support on Windows and macOS
• Fantastical: syncs with any CalDAV service
• Morgen: works with iCloud, Fastmail, and other CalDAV servers

You pick the server for privacy. You pick the client for usability. That’s the beauty of an open protocol.

Conclusion

Proton Calendar CalDAV support doesn’t exist – and the reason is a real architectural trade-off. But you don’t have to give up flexibility for privacy.

Mailfence gives you full CalDAV sync and end-to-end encrypted email, all protected by Belgian privacy law. It works with the apps you already use, on the free plan.

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