Privacy Policy
Effective date: August 14, 2026
SentSonar is a Chrome extension that adds read tracking to email you send from Gmail. This policy describes exactly what data the extension and our servers process. We wrote it to be read, not skimmed.
The short version
- We never see your email content, subjects, or recipient addresses.
- We never store full IP addresses of anyone who opens your email.
- The extension has no accounts and no analytics — it never reports your activity anywhere but our own open-tracking API.
- We never access the Gmail API or request Gmail OAuth scopes.
What the extension does in your browser
The extension runs only on mail.google.com. When you send a tracked email, it inserts a one-pixel image into the message body. Everything it knows about your messages — subjects, threads, which badge belongs where — stays in your browser’s local extension storage. On first run the extension generates a random install identifier and a cryptographic keypair used to sign its requests to our API. No name, no email address, no account.
What our servers receive
When a recipient’s mail client loads the tracking pixel, our server (Cloudflare Workers) receives a standard HTTP image request. From it we derive and store:
| Stored | Detail |
|---|---|
| Message token | An opaque random identifier. It reveals nothing about the email. |
| Timestamp | When the open occurred. |
| Classification | human confirmed / human likely / machine / unknown, plus a machine reason. |
| Network prefix | The opener’s IP reduced to a /24 (IPv4) or /48 (IPv6) prefix. The full IP is used once, in memory, to classify the open, then discarded. It is never written to storage or logs. |
| Network owner & country | ASN, network organization name, and country code. |
| Client family | A reduced user-agent family (e.g. “Gmail image proxy”, “Apple Mail privacy proxy”). The raw user-agent string is discarded. |
What we never collect
- Email subjects, bodies, attachments, or headers.
- Recipient email addresses or names.
- Full IP addresses (of you or of recipients).
- Raw user-agent strings or browser fingerprints.
- Your browsing history or anything outside mail.google.com.
Recipients’ data
Recipients of tracked email are the people whose opens we process. We minimize this to the reduced network and client data in the table above, retained for 90 days and then deleted. Unmatched open events are deleted after 7 days. If you want your recipients to know about tracking, the extension offers a disclosure footer; it defaults to on for EU/UK recipient domains.
Notifications
Notifications are delivered by Web Push and fire only for human-classified opens. Machine and unknown opens never generate notifications.
This website
This site is static and fonts are self-hosted. It uses Google Analytics (measurement IDG-PTBZG19KP3) to count page views, which sets Google Analytics cookies in your browser. That is the only third-party code on the site, it is not present in the extension, and it is never joined with email open data.
Chrome Web Store limited use
Our use of data obtained through the extension complies with the Chrome Web Store User Data Policy, including its Limited Use requirements. Data is used solely to provide the read-tracking feature you see, is never sold, never used for advertising, and never transferred except as required to operate the service (Cloudflare, our hosting provider) or to comply with law.
Your choices
- A global kill switch in the extension popup disables all tracking instantly.
- Per-account toggles disable tracking for individual Gmail accounts.
- Uninstalling the extension stops all data collection immediately.
- To delete server-side data for your install, contact us with your install ID (shown in the popup) at admin (at) sentsonar (dot) com.
Changes
If this policy changes materially, the extension will show a notice before the change takes effect. The current version is always at this URL.
Contact
admin (at) sentsonar (dot) com