Include the extension version (Settings → About) and your Firefox or Chrome version when reporting bugs.
A personal note from the maker
For years, I relied on Google Workspace for my email and calendar. Over time, Google kept adding features I didn't need — and raising the price to match. That alone wasn't a dealbreaker. What really got me thinking was the growing European push for digital independence from US tech giants. I wanted to see if I could do the same.
So I went looking for a European alternative that ticked my boxes: custom domain support, enough storage, a decent interface, and simplicity. That search led me to Proton. Based in Switzerland, end-to-end encrypted, privacy-first — it looked like exactly what I needed. I subscribed and migrated.
— And then reality hit. —
The first time I set up Proton on my Android phone, I discovered that my contacts wouldn't sync with any other app — they were locked inside Proton's own apps. Same story for the calendar: my trusted calendar app was useless, because Proton Calendar only works through Proton's app. On the desktop side, I had been relying heavily on a Firefox extension called Checker Plus for Gmail to manage my inbox — and of course, nothing like that existed for Proton Mail.
I reached out to Proton about these gaps, but there were no immediate plans to address them on Android. Instead of crawling back to Google, I decided to build what was missing myself.
That's how Mail Checker for Proton Mail and Sync Provider for Proton were born — out of my own frustration and my own need. I use both of these apps every single day. The motivation to keep them running, maintained, and improving is deeply personal:
I am my own biggest user.
That said, I genuinely hope Proton will fill these gaps themselves one day — especially on the sync side. They have the team, the resources, and the expertise to do it far better than I ever could. If that day comes and Sync Provider for Proton becomes obsolete, I won't be sad. Quite the opposite — I'll be thrilled.
A feature-rich browser extension that lets you read, compose, and manage your Proton Mail right from the toolbar — without ever opening a tab.
Screenshots
Scroll → · click to zoom
📩 Inbox at a Glance
- Unread count badge on the toolbar icon
- Message list with sender, subject, time & preview
- Full message preview without leaving the popup
- HTML, plain-text, and raw view (with optional HTML prettify)
- Decrypt attachments — open in a new tab or download
- Verification code detection — auto-extract OTP/2FA codes with click-to-copy badge; customizable regex patterns
- Configurable preview lines (0–10) and max messages per account
- Sender display format: name, email, or both
👥 Multi-Account
- Monitor multiple Proton Mail accounts simultaneously
- Per-account folder monitoring
- Quick account switching with account pills
- Custom account labels, colors, and drag-to-reorder
- Account alignment with Proton web slots
- Separate notification settings per account
✎ Compose & Reply
- Full email composition directly in the popup
- Reply, Reply All, and Forward
- Rich text editor with formatting, colors & links
- Default compose format & reply format (HTML or plain text)
- Open compose in popup or redirect to Proton web
- File attachments, drag-and-drop
- Image attachment mode: inline, attach as file, or both
- Optional "Send & Archive" button
- Draft auto-save and persistence
- Contact autocomplete for recipients
- Spellcheck support (uses browser dictionaries)
⚡ Quick Actions
- Mark as read/unread, star, archive, trash
- Permanently delete (skips Trash, with confirmation)
- Move to folder and apply labels
- Snooze messages (1 h, 3 h, tomorrow, next week)
- Report phishing, view headers & details
- Drag-to-reorder and show/hide individual actions
🔔 Notifications & DND
- Desktop notifications for new mail
- Toggle message preview text in notifications
- Configurable sounds (chime, bell, ding) with volume
- Notification click actions (open message, open inbox, or do nothing)
- Custom badge color
- Do Not Disturb with preset durations
- DND icon indicator
📅 Calendar Integration
- Detect calendar invitations in messages
- RSVP directly (accept, tentative, decline)
- View attendee status for each event
🎨 Themes & Customization
- Three UI themes: Classic, Modern, Material
- Light, Dark, and Auto color schemes
- Adjustable popup width (350–800px) and height (300–600px)
- Pop-out the popup into its own detachable window
- Display density: Comfortable, Cozy, Compact
- Custom CSS injection with current-CSS export
🔒 Security & Privacy
- SRP authentication — password never leaves your device
- Two-factor authentication (TOTP) and FIDO2 security keys
- Two-password account support (separate mailbox password)
- Show / hide eye toggle on every password field
- OpenPGP message and attachment decryption
- Encrypted session keys stored in browser
- Communicates only with *.proton.me
🛠 Behavior & Automation
- Auto-mark-read on preview, reply, archive, delete…
- Auto-advance to next message after action
- Cross-account and wrap-around navigation
- 12- or 24-hour time format
- Adjustable polling interval (30 s – 60 min)
- Automatic background sync via Proton's event system
🌐 Languages & Data
- Translated into 28 languages
- Settings export & import (JSON)
- Browser sync for cross-device settings (Firefox sync & Chrome sync)
- Mailto: handler registration
- Debug logging for troubleshooting
Exactly what lives where
Here's what the extension stores, and where. All traffic goes to Proton's servers except for hCaptcha (during human verification) and a small license-check endpoint for Pro subscriptions. No analytics, no telemetry.
- Mailbox key password (used to unlock your PGP keys)
- Access and refresh tokens
- Account metadata: email address, user ID, display name
- Message metadata: unread counts, message IDs, folder state
- Your preferences and settings
- Your decrypted PGP private keys
- Decrypted message bodies and 500-character preview snippets used by the popup
- Contact data used for recipient autocomplete when composing (per-account cache, 5-minute time-to-live)
- Attachments (fetched on demand, never cached)
Security boundary. The encryption key for the at-rest secrets is stored in the same browser-storage area, so this protects against casual profile inspection and accidental exposure in backups, but not against malicious browser extensions or a compromised user profile. If that's in your threat model, Proton Mail in a private browser profile with only vetted extensions is the stronger choice.
Want stricter isolation? If you'd rather have no Proton data touching local extension storage — or any other link in the chain between you and Proton — use Proton Mail's web interface directly, which keeps everything in the tab session only. You give up popup convenience in exchange for zero additional trust.
Free & Pro
Use the free version indefinitely or upgrade to Pro for the full experience.
Free
€0 — forever
- Single Proton account
- Unread count badge & message list
- Message preview (plain text only)
- Basic desktop notifications
- Default theme only
- End-to-end encryption
Pro
€2 / month or €22 / year (incl. VAT, price might vary by country)
- Everything in Free
- Unlimited accounts with per-account folders
- Full compose, reply, reply-all & forward
- Rich text editor with attachments
- All quick actions, including permanent delete
- Verification code detection with customizable regex
- Calendar invitation RSVP & attendee status
- Notification sounds, click actions & DND
- HTML & raw message view, attachment open & download
- Light, Dark & Auto color schemes, three UI themes, density & custom CSS
- Settings export, import & browser sync (Firefox & Chrome)
- Two-factor authentication (TOTP & FIDO2 security keys)
- Mailto: handler registration
- … and every other feature listed above
- All future updates included
One subscription is for a single person. For team, family or business use, contact me.
Payments processed by Paddle.com, our Merchant of Record.
Features and pricing are indicative and subject to change until final release.
A native Android sync adapter that brings your Proton Contacts and Proton Calendar to every app on your phone — fully encrypted, fully offline-capable.
Screenshots
Scroll → · click to zoom
👤 Contacts Sync
- Full two-way sync with Proton Contacts
- All fields: name, email, phone, address, photo, birthday…
- Contact groups / labels
- Works with Samsung Contacts & Google Contacts
- Intelligent conflict detection with resolution UI
- Incremental sync — only changed contacts are fetched
📅 Calendar Sync
- Full two-way sync with Proton Calendar
- Events, all-day events, time zones, locations, descriptions
- Full recurring event support (RRULE, RDATE, EXDATE)
- Edit single occurrence, this-and-future, or entire series
- Reminders / alarms mapped to Android notifications
- Multiple calendar support with colors
👥 Attendees & Invitations
- Attendee management with participation status
- Send invitation, update, and cancellation emails
- Poll attendee responses (accepted / declined / tentative)
- Organizer details and roles
🔒 Security & Authentication
- SRP 6a — password never transmitted in plaintext
- Two-factor authentication (TOTP)
- Hardware-backed Keystore for credentials
- AES-256-GCM encrypted local token storage
- OpenPGP encryption for all contact & calendar data
- No analytics, tracking, or third-party data sharing
🔄 Sync Framework
- Configurable intervals: 15 min, 30 min, 1 h, 4 h, or custom
- Manual sync and full re-sync (Remote→Local / Local→Remote)
- Lightweight event-loop poller between full syncs
- Background WorkManager with battery-optimization guidance
- Separate intervals for contacts and calendar
👥 Multi-Account
- Multiple Proton accounts on one device
- Per-account sync settings and intervals
- Per-account enable/disable for contacts & calendar
- Custom display names per account
- Easy re-authentication and account removal
⚙ Settings & Configuration
- Card-based, collapsible per-account settings
- Calendar sync timeframe (past & future days)
- Exclude external / subscribed calendars
- Notification-on-failure toggle
- 25 languages supported
📋 Diagnostics & Logging
- Real-time sync log viewer with auto-scroll
- Copy and export logs for troubleshooting
- Sync trigger labeling (Manual, Scheduled…)
- Detailed encryption and network request logs
Exactly what lives where
Here's exactly what lives where on your device, so you can decide if the trade-offs fit your threat model. Nothing on this list leaves your device except via Proton's own API — there are no analytics, no crash reporters, and no third-party destinations.
- Mailbox passphrase — hardware-backed on supported devices
- Access and refresh tokens — in Android's
AccountManager, with file-based encryption when the device is locked - Decrypted PGP keys — never persisted; re-unlocked fresh on each sync
- Synced Proton contacts — written to Android's standard
ContactsProvider, same place your Google and Samsung contacts live - Synced Proton calendar events — written to Android's standard
CalendarProvider, same place your other calendars live
- Decrypted contact and event content during the sync cycle (released as soon as sync finishes)
- Unlocked PGP private keys
Why plaintext at all? This is the whole point of a native sync adapter: once decrypted, your Proton contacts show the right name when someone calls you, and your Proton events appear on your watch, your lock screen, and in whatever calendar app you prefer. If the data stayed encrypted inside the app, none of that would work. The same security model applies to every sync adapter on Android — Google, Samsung, iCloud, DAVx5. The at-rest protection above guards against casual disk inspection, backups, and apps without the right permissions; it does not protect against a rooted device or a malicious app that already has READ_CONTACTS / READ_CALENDAR.
Want stricter isolation? If you'd rather have no data touching Android's system providers — or any other link in the chain between you and Proton — stay with Proton's official Android apps, which keep everything in-app. You give up system-wide integration in exchange for zero additional trust.
7-Day Free Trial
Try every feature free for 7 days — no commitment, cancel anytime.
- Unlimited Proton accounts with per-account settings
- Two-way Contacts sync (all fields, groups, photos)
- Two-way Calendar sync (events, time zones, locations)
- Full recurring event support (RRULE, RDATE, EXDATE)
- Reminders & alarms mapped to Android notifications
- Custom sync intervals & event-loop polling
- Calendar sync timeframe (past & future days)
- Attendee status polling
- Send invitation, update & cancellation emails
- External / subscribed calendar control
- Full re-sync (Remote→Local / Local→Remote)
- Sync log viewer & export
- End-to-end encryption (OpenPGP)
- All future updates included
Available on the Google Play Store. Payments handled by Google Play.
Features and pricing are indicative and subject to change until final release.
Support
Direct email support for both apps. Replies are personal — no ticketing systems, no chatbots.
Include your Android version, device model, and the app version (Settings → About) when reporting bugs.