Syntax and structure
Addresses are parsed against RFC rules — malformed local parts, illegal characters and oversized domains are rejected before they ever reach your sending platform.
No signup · Nothing storedCut the addresses
Cut the addresses
that will bounce.
A bad list does quiet damage — bounces climb, inbox placement slips, and by the time you notice, your sender reputation is already paying for it. MailProof finds the addresses that cannot receive mail — dead domains, disposable providers, typos, role inboxes — and tells you exactly what it found. It checks the domain, not the mailbox, and it never pretends otherwise.
8signals per address
~350disposable providers
0records retained
mailproof · results
ada@stripe.comDomain OK70Domain accepts mail — mailbox not confirmed
info@acme.ioRisky40Role address — reaches a shared inbox
grace@gmial.comUndeliverable0Domain does not exist — did you mean gmail.com?
test@mailinator.comUndeliverable5Disposable address — designed to expire
What we check
Eight signals, and the reasoning behind each one.
A status on its own is a verdict without evidence. Every result MailProof returns carries the finding that produced it, so you can decide what your list actually needs.
Domain and MX records
We resolve the domain live and read its mail exchanger records. A domain with no MX cannot receive mail, and we say so plainly rather than guessing.
Disposable providers
Nearly 350 throwaway providers are matched on sight — Mailinator, Guerrilla Mail, 10MinuteMail and the rest. These addresses expire by design and never convert.
Role accounts
info@, sales@, support@ and their siblings land in shared inboxes. They inflate complaint rates and rarely belong on a marketing list, so we flag every one.
Typo detection
gmial.com, hotmial.com, yahooo.com. We measure edit distance against the domains people actually mistype and hand back the address they meant to enter.
Mail platform
We identify who really runs the mailbox — Google Workspace, Microsoft 365, Proofpoint, Mimecast — so you know what sits between you and the inbox.
How it works
Three steps, no account.
01
Bring your list
Paste addresses straight in, or drop a CSV or Excel export. Every column is scanned, duplicates are stripped, and you keep the original file.
02
Watch it resolve
Checks run in parallel and stream back as they land. Nothing sits behind a queue, and you can stop a run at any point without losing what has finished.
03
Export what is clean
Filter to deliverable, risky or undeliverable, then export a CSV carrying the score and the evidence for every decision.
Why it matters
Bounces are not a rounding error.
Mailbox providers treat a high bounce rate as a signal that you do not know who you are writing to. Cross the threshold and the penalty is not a warning — it is quieter delivery, for every campaign, including the ones to people who wanted to hear from you.
- Above 2% bounces and most ESPs start throttling. Above 5%, some suspend the account outright.
- Reputation is slow to rebuild. A single bad import can shape placement for weeks after you have fixed the list.
- Role and disposable addresses drive complaints and skew every metric you use to judge a campaign.
Bounce rate7.4%
Unverified list — sending paused by the provider
Bounce rate0.6%
Same list, verified and cleaned first
Questions
The things people ask first.
Does this tell me whether a specific mailbox exists?
No, and you should be sceptical of any tool that says it does. We check the domain: syntax, live DNS, MX records, disposable providers, role accounts and typos. We do not check the part before the @. That means a real address and an invented one at the same working domain get the same result — because from the outside they are genuinely identical. Confirming a mailbox needs an SMTP probe, and on Google Workspace, Microsoft 365 or any catch-all domain even that answers "accepted" for every address before bouncing privately later. So the best status we offer is "Domain OK", never "Deliverable".
Then what is it actually good for?
Removing the addresses that will certainly bounce, which is where the reputation damage comes from. Dead domains, disposable providers, malformed addresses and typo domains are all provably undeliverable, and those are the ones that hurt you. Role inboxes get flagged because they drive complaints. What is left is a list worth sending to — not a list of confirmed humans, and we do not label it as one.
What happens to the addresses I upload?
They are held in memory for the length of the request and then discarded. Nothing is written to a database, nothing is logged, and nothing is shared. Close the tab and the run is gone.
How large a list can I verify?
Files up to 10 MB, or roughly 50,000 addresses per upload. The list is processed in batches so a slow domain never stalls the rest of the run.
Why does a valid-looking address come back as risky?
Risky means the domain accepts mail but something about the address should give you pause — a shared role inbox, a likely typo, or a domain that resolves without a mail server. It is a signal to look, not an instruction to delete.
Is there an API?
Yes. Single and batch endpoints, JSON in and JSON out, no key required while the service is in open preview. The reference is on the API page.
Find out what your list is really worth.
Paste ten addresses or upload fifty thousand. No account, no card, nothing kept.