Imagine you’re mid-flight, tray table down, coffee gone cold, and — of course — your phone buzzes with an important thread. Until today, encrypted email apps tended to treat offline as a second-class citizen: you could maybe see a cached message or two, but composing, organizing, and fully working your inbox without a connection was clunky or impossible. Proton wants to change that.

On September 25, 2025, Proton published a major update to its Mail apps for iOS and Android that rebuilds the mobile experience from the ground up. The headline: a full offline mode that lets you read, write and organize emails without an internet connection, with everything syncing automatically once you’re back online. Proton says the change is part of a larger rewrite that moves the apps to a shared codebase and focuses squarely on speed and parity across platforms.

What’s actually new

• Offline mode — You can now open, compose and manage messages while offline; changes sync when connectivity returns. That’s the central change Proton is pitching as making the app genuinely usable on trains, flights, or in dead-zone corners.
• A redesigned layout — The app’s look is cleaner and the Compose button has been moved from the top-right to the bottom of the screen to be easier to reach with your thumb. Proton frames the redesign as ergonomics more than cosmetics.
• Speed improvements — Proton claims routine actions — scrolling, archiving, replying — are “twice as fast” compared to the previous app.
• Feature parity across iOS and Android — Android users finally get tools they’d seen on iOS for a while, like snooze and scheduled messages; Proton says both platforms will now ship the same features at the same time.

The engineering story: why Proton rebuilt the app

Proton says this is more than a visual refresh. The company rewrote its mobile stack — using Rust for shared logic — so iOS and Android now share roughly 80% of their code. The payoff is twofold: faster day-to-day performance on devices, and faster rollout of new features on both platforms simultaneously. Proton calls the release “v7” of Mail and positions it as a foundation for future work (including faster Calendar updates).

Why Rust? In Proton’s telling, Rust lets them move complex logic out of platform-specific code while keeping native performance; that’s how they can claim both “native speed” and a high degree of shared code across systems.

The privacy tradeoffs — what you should know

Offline features always mean one extra thing: data has to live on your device. Proton emphasizes that it’s preserving its “best-in-class privacy and end-to-end encryption” while delivering offline access, and the blog post frames the change as privacy-forward rather than privacy-compromising. The company’s post, though light on low-level implementation detail in the announcement, promises further technical write-ups soon. If you care about what’s stored locally (how it’s encrypted, how long it persists, whether attachments are cached), look for Proton’s follow-up docs or their technical write-up when it appears.

Early user reporting suggests there are practical limits to how “complete” offline really is right now. Threads on the Proton subreddit and other communities note that offline access currently behaves like a smart cache: it will let you read and compose messages you’ve recently accessed or that the app cached, but it might not let you search across your entire mailbox offline or load messages you’ve never opened on that device. Those are important caveats for anyone expecting a full server-side replica on their phone. Treat offline use as a big usability boost, not a full local mirror — at least until Proton’s docs or subsequent updates clarify otherwise.

How does this compare to other mail apps

Mainstream apps like Gmail and Apple Mail have historically offered various offline capabilities (Gmail’s web offline mode, local caching on iOS), but Proton’s pitch is different: encrypted email plus purposeful offline functionality. For privacy-minded users who’ve tolerated slower mobile clients in exchange for encryption, Proton’s move narrows the gap between convenience and privacy. External press coverage focused on that tension — Proton arguing you shouldn’t have to “choose between Big Tech’s convenience or encrypted email’s privacy.”

Who wins from this update

• Frequent travelers and commuters who need to triage and compose while offline will benefit most.
• Privacy-minded users who wanted an encrypted mail client that didn’t feel slow or dated.
• Android users now get parity for features like snooze and scheduled sending.

How to get it

Proton says the apps are rolling out now (Sept 25, 2025). iOS users can update via the App Store; Android updates should arrive through the Play Store as the staged rollout widens.

Proton’s update is less a cosmetic refresh and more a strategic pivot: rebuilt mobile clients, a focus on native performance, and a practical offline mode that brings encrypted mail closer to the convenience of mainstream providers. There are early caveats — notably around how much of your mailbox is actually available offline and the details of local storage — but for many users, this will feel like a long overdue modernization. Proton has matched a privacy promise with a usability push; now the real work is proving the model in day-to-day use and being transparent about what the offline cache holds and how it’s protected.