See mailshade.org

Open source email tracker blocker

A tool that sits inside your inbox to stop tracking is only trustworthy if you can read what it actually does — and most tracker blockers are closed. PixelBlock and Gblock ship no source; you take their behaviour on faith. For a privacy extension, that is the wrong default. Mailshade publishes its full source under AGPL-3.0 at github.com/mailshade/mailshade, so anyone can verify that it blocks tracker requests at the network layer via declarativeNetRequest, that blocked events stay in local IndexedDB, and that nothing about your inbox is sent to a server. Open source is also how you confirm the privacy claim is real rather than marketing: there are no analytics and no backend handling your mail, and the code is the proof. Mailshade covers six web clients — Gmail, Outlook, Office 365, Superhuman, Yahoo Mail and ProtonMail — and is actively maintained, unlike some open-source blockers that have gone stale.

Why open source matters for a tracker blocker

An extension with inbox access can see message content. Closed source means you cannot check what it does with that access. AGPL-3.0 source means the blocking logic, the storage, and the network calls are all readable — you can confirm the tool only cancels tracker requests and keeps data on-device.

Open-source options compared

  • Ugly Email: open source, but Gmail-only and warns rather than blocks; little maintenance since 2022.
  • Trocker: open source, covers Gmail, Outlook and Yahoo, but no Superhuman and only a blocked count.
  • Mailshade: AGPL-3.0, six clients, network-level blocking via DNR, per-sender reporting in IndexedDB, click-tracker unwrapping.

What you can verify in Mailshade's code

That it uses declarativeNetRequest rules to cancel pixel requests, that blocked-events and block-lists are written only to IndexedDB, and that the sole outbound call is the Polar checkout for a license — no telemetry.

FAQ

Is Mailshade really open source?

Yes. The complete source is published under AGPL-3.0 at github.com/mailshade/mailshade. You can read the blocking rules, the storage layer and every network call before installing.

Which other email tracker blockers are open source?

Ugly Email and Trocker are open source; PixelBlock and Gblock are closed. Among the open ones, Mailshade covers the most clients and is actively maintained.

What does AGPL-3.0 mean for me as a user?

AGPL-3.0 is a copyleft licence: the source must stay open, including for any hosted version. For you it means the code is permanently auditable and cannot quietly become a closed, data-collecting build.

Does open source mean Mailshade is free?

No. Open source and price are separate. Mailshade's code is free to read and audit under AGPL-3.0, while the licence to use it is paid, starting at $3.99 per month or $19 one-time.

Can I confirm Mailshade sends no inbox data anywhere?

Yes. Because the source is open, you can verify that blocked events and block-lists are written only to local IndexedDB and that the only outbound request is the Polar checkout, not any analytics endpoint.