Mail Checker for Proton Mail by beo

Mail Checker for Proton Mail, your encrypted inbox directly in the browser toolbar. Read, write and manage your Proton Mail without keeping a Proton tab open.

Items marked * are part of Pro. Everything else works on the free plan: one Proton account, a 15-minute check interval, the unread-count badge and message list, reading messages as plain text, desktop notifications for new mail, sign-in with two-factor authentication or a hardware security key, and .eml export without attachments. A 14-day Pro trial is included, so you can try everything first.

Reading your mail

• Unread-count badge and message list
• Preview lines under each message in the list, and how many messages each account shows *
• Multi-account support, with per-account labels, colors, ordering and a choice of which folders each account watches *
• Read messages right in the popup, as plain text
• HTML and raw source views, with remote images blocked until you choose to load them *
• OpenPGP attachment decryption, click to open in a new tab or download *
• Export any message as a standard .eml file (with Pro, including all its attachments)
• Reading-pane background switch (automatic, light or dark) for awkwardly styled mail *
• Sender logos (BIMI) through Proton's image proxy, with an optional fallback to the sender's own favicon (both off by default)
• Calendar invitations detected in place, with one-click RSVP (Yes / Maybe / No) and add-to-calendar *
• Verification codes detected in the message list, copied with one click
• Edit the verification-code patterns, add your own regular expressions, or switch detection off *

Writing mail

• Reply, reply-all, forward and compose, with attachments by drag and drop *
• Rich text editor with a formatting toolbar *
• Proton AI writing assistant (Scribe) in the reply and compose editors; requires Scribe in your Proton plan, set to run on Proton's servers *
• Share files as Proton Drive links instead of attaching them, with Viewer or Editor permission, an expiry date and an optional password. A way around the 25 MB attachment limit *
• Schedule send, to deliver a message at a future date and time *
• Expiring messages, including password-protected Encrypted Outside for recipients who don't use Proton *
• Contact autocomplete, draft auto-save, spellcheck and an optional "Send & Archive" button *
• Default compose and reply format (HTML or plain text), compose in the popup or in Proton web, image-attachment mode (inline, attach, or both) *

Notifications, and peace and quiet

• Desktop notifications for new mail, with the sender, the subject and a preview of the text
• Custom notification sound, volume, click action and preview-text toggle *
• Custom toolbar badge color *
• Quiet mail rules, to mute the mail you don't want to be interrupted by. Match on sender address, sender name, recipient, subject or body (regular expression), then switch off the desktop notification, the unread count or the sound, or hide that mail from the list entirely. Rules are named, collapse to one line each, and a "Test" button shows what a rule would catch before the next message even arrives. *
• Do Not Disturb mode, and message snooze (1 hour, 3 hours, tomorrow, next week) *
• Configurable check interval; the free plan checks every 15 minutes *

Quick actions from the popup

• Mark read or unread, open in Proton Mail, and export as .eml (on any plan)
• Archive, delete, delete permanently, star, label, move to folder, snooze, report spam or phishing, view headers, message details *
• Drag to reorder the action buttons, and choose which ones show on hover and which go in the overflow menu *
• Auto-mark-read on actions, auto-advance to the next message, cross-account navigation *

Appearance

• 19 themes (Classic, Modern and Material plus 16 color and layout themes), each in Light, Dark or Auto *
• Adjustable popup size and display density, and a pop-out detachable window *
• Custom CSS injection *
• 12- or 24-hour time, and your choice of sender display format *
• 28 European languages

Security and privacy

• End-to-end encryption for Proton-to-Proton messages
• SRP login: your password never leaves your device
• Beta support for Proton's post-quantum encryption keys (RFC 9980)
• Two-factor authentication: TOTP authenticator apps and FIDO2 / WebAuthn security keys
• Mailbox-password (two-password) account support
• Credentials and unsent drafts encrypted at rest on your device (AES-256-GCM)
• No data collection, no analytics, no telemetry. The extension talks to Proton's servers directly. The only other server it contacts is the Pro license check, which receives only your subscription ID (or the transaction ID from your invoice) and never any mail data. Proton's human verification can load its CAPTCHA, and remote images or sender favicons load only if you allow them
• Settings sync across devices via your browser's built-in extension sync *
• Settings export and import as JSON *
• Handler for mailto: links, so Firefox can open them in Proton Mail on the web

The full source code is public at https://github.com/bolausson/mail-checker-for-proton-mail under the PolyForm Shield License 1.0.0, a source-available license.

Mail Checker for Proton Mail is an independent project and is not affiliated with, endorsed by, or officially connected to Proton AG. "Proton" and "Proton Mail" are trademarks of Proton AG.

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Support: support+mcpm@olausson.de