Contact List Reality Check

No. Your list is read and analyzed entirely in your browser — the email addresses are never sent to us or anyone else, there's no account, and nothing is stored. You can verify it yourself: open your browser's DevTools, watch the Network tab, and you'll see that no request contains an email address.

For each unique domain in your list — the part after the @, like gmail.com — your browser asks Cloudflare's public 1.1.1.1 DNS resolver whether that domain has a mail server, exactly as any mail server does before delivering a message. Only the bare domain name is sent, never an email address, and the query goes to the public resolver, not to us.

An address that is syntactically valid, not a duplicate, not on a disposable/burner domain, and whose domain actually exists and can receive mail. It excludes anything that would hard-bounce or that you shouldn't be mailing.

Two ways. First, those tools upload your list to their servers; we never do — everything runs on your device. Second, we connect list health to your sending posture (authentication, reputation, monitoring), so deliverability is one picture instead of two disconnected silos.

Role addresses are shared functional mailboxes like info@, sales@ or noreply@ — they complain more and engage less. Disposable addresses use throwaway or burner domains. Dead domains have no mail server or don't exist at all, so mail to them hard-bounces. Each one drags your sender reputation down.

A surprising amount — and it never leaves your browser. From the part before the @ we flag number-heavy names (like user48213@), which are usually scraped or machine-generated rather than real people, and we show how many read as a named person (first.last style). From the domain we identify the mail provider — including privacy-first mailboxes like Proton and Tuta, which are hidden by design: they block open/click tracking and filter strictly, so authentication matters more for them and engagement metrics under-report.

No. New top-level domains are perfectly valid — plenty of real people and companies use them — so we don't flag them as problems. The only domain-name pattern we call out is punycode / IDN (xn--) domains, because those can be look-alikes of a well-known brand and are worth a human glance.

Not here — and not honestly from the browser. This tool tells you what it can prove on your device: syntax, duplicates, disposable and role addresses, and whether a domain can actually receive mail. Confirming that an individual mailbox exists needs live SMTP probing, and spam-trap detection needs data no single list can see — so we don't guess at them or show fake confidence.

You can analyze a list of any size in your browser. To keep the check fast, domain-existence lookups are capped at a few thousand unique domains — the result tells you when a cap was hit and how many domains it skipped.