Verify an email list without uploading it

Split verification into two questions. Can this domain receive mail? is answered by public DNS and can run entirely in your browser. Does this specific mailbox exist? requires talking to the receiving server, which means sending the address to it — there is no way around that.

So “verify without uploading” is achievable for domain-level checks, duplicates, typos and disposable detection, and impossible for mailbox existence. Any tool that claims otherwise is either doing less than it says or sending your data without telling you.

What runs locally

Parsing CSV, TSV, or pasted text
Normalisation, dedupe, Gmail alias collapsing
Typo repair against provider names
Role and disposable classification by domain
MX lookups via DNS-over-HTTPS — the query contains a domain, never an address

What cannot run locally

Mailbox existence (an SMTP RCPT TO probe), mailbox-full status, and catch-all detection. All three require a server to make a connection and interpret the response, and all three involve revealing the address to at least the receiving mail server — which is fine, because that server already knows about its own users.

Why the distinction matters commercially

Uploading a client list to a random website is a data transfer with real obligations: GDPR processor terms, breach exposure, and whatever your NDA says. Domain-level checking avoids that entirely and removes the largest single cause of bounces — dead domains and typos.

If you genuinely need mailbox-level certainty, pay a per-address verifier and sign the paperwork. For most list cleanups, the domain pass is the 80% that costs nothing.

Check your own list in about 30 seconds. Paste or drop a CSV — duplicates, typos, role addresses and dead domains, all handled in your browser. Free for the first 100 addresses, $19 once for unlimited.

Open the tool

Common questions

Doesn't Google see my lookups anyway?

Google sees that someone asked whether a domain has MX records — the same query any mail server makes when delivering. It does not see the list, the addresses, or which rows you kept.

Can a browser tool check SMTP?

No. Browsers cannot open raw SMTP connections, which is exactly why mailbox-level verification has to be server-side.

Last updated 2026-10-23.