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 mailshade.org/source/, so anyone can verify that it blocks requests to known tracker-pixel domains via declarativeNetRequest, keeps tracker history in local IndexedDB, syncs settings through Chrome Sync, and does not transmit core inbox history to Mailshade servers. The source also exposes paid auth/Polar calls and the optional privacy-filtered Hawk crash-report path, which is off by default. 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 makes the blocking logic, storage, Chrome Sync settings, paid calls and optional crash reporting readable. Each mail client is opt-in.

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 known-domain blocking via DNR, per-sender detection history in IndexedDB, local click-tracker detection with a direct-or-original choice.

What you can verify in Mailshade's code

DNR cancels requests to known tracker-pixel domains. DOM scanning detects pixels and tracking links in opened messages. Stored events keep the tracker origin, sender and opaque message context — not full tracker URLs — and core inbox history is not transmitted to Mailshade servers. Paid actions contact Mailshade's auth service and Polar; privacy-filtered Hawk crash reports are optional and off by default.

FAQ

Is Mailshade really open source?

Yes. The complete source is published under AGPL-3.0 at mailshade.org/source/. 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 published release remains auditable, and distributing a modified covered version or offering it over a network carries corresponding-source obligations under the licence.

Does open source mean Mailshade is free?

Open source and price are separate. Mailshade's code is free to audit under AGPL-3.0, and core protection remains free after a 14-day Pro trial. Paid Pro starts at $3.99 per month or $19 one-time.

Can I confirm Mailshade sends no inbox data anywhere?

Yes. The source shows that core inbox history stays in local IndexedDB rather than going to Mailshade servers. It also shows Chrome Sync for settings, paid auth/Polar calls, and optional privacy-filtered Hawk crash reports that are off by default.