A leaked Resend key emails as your domain
Exposed email-provider keys send mail from your verified domains — deliverable, signed, trusted. Scan your app free.
Email keys buy more than send quota: they buy your reputation, since mail goes out authenticated as your domain — landing in inboxes, not spam.
What a Resend API key is
re_…_… keys authenticate Resend sends from your verified domains, inheriting SPF/DKIM alignment.
re_FAKE_000000000000000000000The prefix is the claim: scanners and attackers alike identify the format before they know anything else about it, which is why recognition starts at the first characters rather than the last.
What it grants
Reputation-forward abuse:
- Phishing campaigns bearing your DKIM signature.
- Contact/suppression list reads where endpoints allow.
How it ends up in a bundle
Three arrival routes cover nearly every case we see:
- Waitlist/notification widgets wired client-side during launch week.
- Contact forms skipping server middleware.
Does it belong in a browser?
Send paths belong server-side exclusively; keys never needed in browser.
Rotate it
resend.com/api-keys → rotate; review recent sends for foreign content; notify affected recipients if phishing occurred.
Find it in seconds
Open DevTools on the deployed site and search the built assets for re_. If the search hits, the credential shipped; if it does not, check the chunks loaded on authenticated or interactive views, not just the landing page — the calling code often sits behind a route.
The faster path is to let a machine do the fetching. KeyDrift downloads the same JavaScript a visitor gets — HTML, every referenced chunk including ones named only in the route manifest, and the server-streamed data frameworks inline into the document — and reports credentials with a masked prefix, a fingerprint, and the exact file they live in. Paste your deployed URL into the scanner; no account needed.
Make sure it stays gone
It bears saying because it happens constantly: the fix holds until the next prompt that needs the query to return rows. Drift monitoring exists for precisely this — it diffs consecutive scans and pages you when a previously resolved finding reappears, naming the regression as a regression rather than repeating the first alert.
The bigger picture
It helps to name the economics honestly. Fixing this class of leak costs minutes when caught at deploy time and days when caught at invoice time, because by then the credential has been harvested, validated, resold or drained — often all four. Detection latency is the entire game, which is why the monitoring half of KeyDrift exists alongside the scanning half.
How KeyDrift reports this exact finding
When KeyDrift finds this on your deployment, the report shows a masked value (first 8 and last 4 characters only), a salted fingerprint for tracking, the exact chunk filename carrying it, and a severity with written rationale. Public-by-design neighbours — anon keys, publishable keys, Firebase web constants — appear as informational context rather than noise, because knowing what should be there is what makes the real findings credible.
Manual check, step by step
A five-minute version you can run anywhere: view-source on the landing page, copy every src= script URL, fetch each and search the results for re_. It misses manifest-only chunks and streamed payloads — which is precisely the gap between "I checked" and "it is clean" — but it catches the loud majority and builds the pattern-recognition that makes scanner output legible.
Close the loop with monitoring
Monitoring closes the loop that one-time verification leaves open. A scheduled scan refetches everything, diffs against history, and fires only on transitions: created, regressed, resolved. Regression alerts matter most here — they fire when a previously fixed finding returns, which in agent-era codebases is less a possibility than a schedule.
Common questions
Deliverability damage reversible?
Gradually — remediate, warm domains, monitor reputation; prevention beats repair.
Suppression lists sensitive?
Often contain customer emails — PII exposure folded into the incident.
Run a free scan at keydrift.dev/scan — paste a URL or the bundle source itself, no account. Findings arrive masked, with the exact chunk they live in.