Sender Guard — Gmail sender verifier

Checks SPF, DKIM, DMARC and sender identity on every Gmail message you open. Runs on your device; no data ever leaves.

Gmail's spam filter catches the obvious. Sender Guard catches the message that looks like it came from PayPal, your bank, or your boss — but didn't. The damage from a phishing email doesn't happen when you read it. It happens when you click the link inside. Sender Guard checks the one thing that decides whether that link is safe: is the sender actually who they claim to be? What it does • Reads the authentication trace. Every message Gmail delivers carries an Authentication-Results header written by Google's own mail servers — SPF, DKIM, DMARC. Sender Guard decodes it and shows you the result as plain evidence, not a green tick you have to take on faith. • Checks alignment, not just "pass". A valid DKIM signature doesn't mean the address is real — an attacker can sign mail from their own domain. Sender Guard checks whether the signature actually belongs to the sender's domain. This is the step most tools skip. • Catches impersonation. Display name says "PayPal" but the address is a Gmail account? Domain is `chase-secure-alerts.com`, or `arnazon.com` with an "rn" standing in for the "m"? Hidden right-to-left characters that flip `invoice‮fdp.exe` into something that reads like a PDF? All flagged. • Uses your own history. "You've exchanged mail with this name before — but from a different domain." Only your inbox can know that, and it's how business-email-compromise gets caught. • Stops the click. On a suspicious message, clicking a link shows you its real destination before the browser opens it. The verdict is about the sender — nothing else. A verified sender stays green even if the newsletter has a tracking link; content notes live in a separate section so the badge never cries wolf. Privacy: nothing leaves your device No OAuth. No Gmail API. No server. No analytics. No external request of any kind. Sender Guard runs inside Gmail with your existing session and reads the same "Show original" source Gmail already exposes to you. Your settings and a small on-device list of past senders are stored locally in the browser and never transmitted. Turn it off and Gmail is never touched. Open source. Free. Built by one person — no ads, no paid tier. *Not affiliated with, or endorsed by, Google. "Gmail" is a trademark of Google LLC.*