What an email check can prove, and what it cannot
A verifier asks a domain about one address. A domain with no mail servers accepts nothing, so anything at it is undeliverable, and that answer is definitive. Most other answers are not. Google and Microsoft tenants with catch-all switched on say yes to every address anybody asks about, so we report that as unproven rather than rounding it up into a pass.
- The one certain no
- A domain with no mail servers
- Catch-all domain
- Accepts everything, proves nothing
- Role mailbox
- Deliverable, and not a person
- Confirming your own address
- Free
No card. Checking addresses you already hold costs nothing.
One answer is certain. The rest are evidence.
Verification is sold as a yes or a no. In practice it produces one reliable no, one meaningless yes, and a lot of results that only mean something next to who has seen the address before.
- A domain with no mail servers is a definitive no
- Nothing can arrive there, however plausible the address looked. It costs no vendor and no probe to establish — the record is public — and it is the one result on this page that needs no qualification.
- The acceptance code that means nothing
- A mail server answering with an acceptance has accepted the conversation, not the mailbox. On a tenant with catch-all on it says exactly the same thing about an address nobody has ever had, so a pass there is a statement about the domain and not about the person.
- Deliverable is not the same as reachable
- info@, careers@, billing@ arrive perfectly well, and nobody behind them will answer a cold pitch. They are shown so you can see they were considered, never promoted to being the answer, and never charged for.
- Unknown is a real answer, and is reported as one
- Sometimes nothing definitive comes back: the host does not respond, or the check cannot be run against it at all. An unknown quietly rounded up to a pass is how a list that looked clean still bounces.
Six results, and what each one is telling you
Keep this next to whatever tool you use. The words are near enough industry standard; what varies between vendors is which of them get quietly reported as a pass.
| Result | What it means | What to do |
|---|---|---|
| Valid | The mailbox was reached and answered for itself, at a domain that does not answer for everybody. | Send. This is as close to certain as this gets. |
| Invalid | The domain takes no mail, or the address was refused outright. | Remove it. It is a bounce with a date on it, and bounces are charged to your sending reputation rather than to a vendor. |
| Catch-all | The domain accepts every address, so the check has established nothing about this one in particular. | Judge it on evidence instead: how many independent sources have seen it. One sighting at a catch-all domain is a lead. |
| Unknown | No definitive answer came back. The host did not respond, or the check could not be run against it. | Treat it as unproven and come back to it. It is not a pass and should never be exported as one. |
| Role | A shared function mailbox rather than a person. | Fine for an enquiry to a company. Wrong for anything addressed to a human being. |
| Disposable | A throwaway provider. Deliverable now, gone shortly, read by nobody. | Drop it, and drop the row it arrived on. |
Most of the market sits behind a door that says yes to everyone
The traditional check works by starting a delivery and stopping before the message: ask the domain whether it will take mail for an address, note the answer, hang up. It was a good test when companies ran their own mail. It is close to useless now that most of them are on Google Workspace or Microsoft 365, where catch-all is common and the answer to every address is the same acceptance.
That is why a verification score on its own is not a number to buy on. A tool reporting ninety-something per cent confidence on a catch-all domain has measured how agreeable the mail host is. It has not found out whether that person reads mail at that address.
Our answer for those domains is smaller and truer. Confidence comes from who has seen the address rather than from the door: sighted twice by unrelated sources and it is verified, sighted once and it is risky and arrives with the sighting attached, derived from a house style at a catch-all domain and it says so. You are told what the evidence is, and you decide whether it is enough to open a domain with.
Checking what you have is the free half of this
A credit buys finding a contact, never agreeing with one. An import of addresses you already hold can be checked end to end without spending anything.
There is no field on this page to paste one address into. A single check, no account, is on the way and is not here yet — and a form that takes an address and emails the answer tomorrow is not the same thing. What works today is the free plan, which takes a list rather than a line, and it is the version you would want anyway once you have more than one address to think about.
- Your column, kept
Bring the list in as it stands
Upload the CSV and map the column your addresses are in. They keep their own label until something is actually known about them — nobody has checked them yet and the screen does not pretend otherwise.
- Confirmation is free
Run it
Each address is checked, and where the check cannot settle it the row is looked up on its own evidence instead. Agreeing with an address you supplied costs nothing at all.
- Two files out
Split the file before you send
Export by state, so the addresses you can send to and the ones that need a judgement are two files rather than one column you have to read row by row.
Free plan: 50 addresses a month, no card, and confirmations on top.
What people ask about checking an address
Does checking an address send the person an email?
No. Nothing is delivered and nobody is notified. A check is a conversation with the domain about whether an address could receive mail, closed before any message is handed over — and where the domain will not answer usefully, we say so rather than sending something to find out.
I already have 4,000 addresses. What does checking them cost?
Nothing, if all we do is agree with them. A credit buys finding a contact you did not have, never confirming one you typed in — and a single-source find on a row you already filled is free too, because we will not swap an address a human vouched for with one nobody has corroborated. Where two independent sources confirm a different address, that is a real find and costs one credit; your original is kept in the row beside it.
How long is a check good for?
Less time than people assume, and we do not publish a fixed expiry because there is not an honest one to publish. A check describes the moment it was made: a mailbox can be closed the week after it answered, a person can leave, a domain can change hands. Re-check a list shortly before you send on it rather than trusting the date it was last looked at.
Can a verifier tell me a mailbox is full, or the person is on leave?
No, and neither can anything else. A check establishes whether an address can receive mail at all. Whether it is read, whether it is a shared inbox somebody left behind, and whether the person still works there are different questions — the last one is what job-change monitoring is for.
Is a disposable address the same as an invalid one?
They fail differently. A disposable address at a throwaway provider usually accepts mail perfectly well and stops existing an hour later, so it is treated as a fail rather than as a pass. An invalid address is one nothing can reach at all — most often a domain with no mail servers behind it.
If a checked address still bounces, was the check wrong?
Sometimes, and the honest answer is that no check is a guarantee. A mailbox can be closed the day after it answered, a filter can reject on reputation rather than on the address, and a domain can change mail provider overnight. Tell us the address and we will look at what was known when the answer was given.