Check a list
Paste addresses (one per line, or a whole CSV — we'll pull the emails out), or upload a file. Your list stays on this device: the only thing that leaves is a DNS lookup of each domain, unless you add your own provider key below.
What the free check proves: an address is well-formed and its domain can receive mail — and it flags likely typos (with a one-tap fix), throwaway domains, role inboxes, free-provider addresses and keyboard-mash names before they cost you. What it can't prove: that the mailbox itself exists — no free check can. A row marked “Domain OK” is not a verified mailbox. Only a provider-key check (ZeroBounce — free key, below) can mark a row ✅ Verified.
Working…
Get a true mailbox check — add your ZeroBounce key
The free checks above prove a domain can take mail — they can't prove a mailbox exists. A provider key proves the mailbox itself, and only rows checked with a key can earn the ✅ Verified label. Verified checks run on the provider's own engine, at the provider's own accuracy — ZeroBounce states 99.6%. Free checks prove the domain layer only.
ZeroBounce — the one we recommend. Have a ZeroBounce key? Paste it and rows get a true mailbox check: mailbox existence and catch-all status, on your own credits. Per ZeroBounce's own site (checked Oct 2026), every free account includes 100 free verification credits a month; signup asks for a business/premium-domain email.
How to get a key: 1) Create the free account. 2) Copy the API key from your account page. 3) Paste it here. With a key in place, every check — one address or a whole pasted list — also runs ZeroBounce's mailbox verification.
Get a free ZeroBounce account →
Other providers work too. Already have a key somewhere else? NeverBounce, Abstract and DeBounce (100 free credits once at signup, then pay-as-you-go at roughly $0.002 a check) plug into the same slot — pick one and paste its key. If a ZeroBounce key is in place, it runs first.
One honest catch: a provider can block calls made straight from a web page (browser security rules). If a call is blocked, the row says so plainly and the mailbox stays unverified. A blocked call is never dressed up as a result.
Your keys are stored only in this browser, are sent only to the provider you picked when you run a check, and never reach us or get logged anywhere.
Results
One tap: that button downloads your clean list and opens MailBook — import the file there and send. No re-typing, no hunting through folders.
Sendable list = just the addresses marked Domain OK or Verified (with names, when your list had them) — the file you import into MailBook. (Risky and Dead stay out.) Full results = every address you pasted, each with its verdict and the reason — dead and risky rows included.
How it works
Paste or upload
Drop in the list you were about to send — a spreadsheet export, an old sphere list, a stack of leads.
We check every address
Format, duplicates, throwaway domains, role inboxes, did-you-mean typo fixes, keyboard-mash flags, and whether the domain can actually receive mail (a live DNS/MX lookup per domain).
Send the clean list
Download the sendable CSV, import it into MailBook, and send knowing the dead addresses were pulled before they hurt your deliverability.
What it checks — honestly
Checked here, for real
- Format — broken addresses never reach a server.
- Duplicates — the same address twice is a bounce-and-spam-complaint risk; extras are pulled.
- Throwaway domains — checked against a built-in list of known disposable domains.
- Dead domains — a live DNS lookup confirms the domain exists and has mail servers (MX). No mail server, no delivery.
- Role inboxes — info@, support@, sales@ and friends get flagged, not silently sent.
- Did-you-mean typo fixes — gmial.com, yahoo.con and friends get a suggested correction with a one-tap fix that re-checks the corrected address.
- Keyboard-mash names — random typed strings in front of the @ get flagged in plain words.
- Free-provider tags — Gmail, Yahoo, Outlook and friends are named on the row, so you know it's a personal inbox, not a business domain.
Needs a provider key
- Mailbox existence — whether this exact inbox is live can't be proven from DNS alone. Anyone who tells you otherwise from a web page is guessing.
- Catch-all domains — some domains accept mail for every address, real or not. Detecting them takes a mailbox-level probe.
- Add your own ZeroBounce key above (free — see the panel; NeverBounce, Abstract and DeBounce keys work in the same slot) and those rows get a real mailbox verdict: ✅ Verified, or ❌ Dead.
Why not just pay DeBounce or ZeroBounce?
- Price: $0, unlimited. No per-check charge, no credit counter — and the warning layer is free here too: typo fixes, throwaway domains, role flags, free-provider tags and keyboard-mash flags, each with the reason printed on the row. One thing that is not free anywhere honest: proving a mailbox on a catch-all domain takes a provider probe — that's what your own key is for.
- Speed: results land on this screen as each check finishes — no upload queue, no hours-long bulk jobs.
- Privacy: your list never leaves this device. The only outbound calls are domain-only DNS lookups — plus a provider check, and only if you add your own key. Both paid services make you upload your list to their servers.
- The honest limit: the paid services also keep server-side spam-trap and toxicity databases. A web page can't copy those, and we won't pretend to — the provider-key bridge above is how you reach that layer when you need it.
Made to sit with MailBook
BounceCheck is the front door for your sending. Clean the list here, then send from MailBook — the paired app lives in the same shelf and there's a BounceCheck entry right inside it, so the flow is: check → clean → send.
Built for realtors working cold and aging lists — expireds, old sphere, bought leads — where a 10–20% bounce rate is normal and every bounce makes the next send land in spam a little more.