You can tell whether an email address is real without sending to it by checking five things in order: the syntax, whether the domain can receive mail, whether the mailbox answers, whether the domain is a disposable one, and whether the server accepts every address (a catch-all). The first four are quick and free. The fifth, catch-all, is why some addresses can never be fully confirmed; across the addresses we verify, about one in forty business domains behaves that way.
A real-looking address and a real address are different things. "[email protected]" can be perfectly formed and still bounce, because the person left, the mailbox was deleted, or the whole domain stopped receiving mail. A fake or mistyped address can also look fine. The only way to know is to check the address against the mail system that would receive it, which is what verification does, without ever sending a message.
That matters because sending to a dead address has a cost. Mailbox providers count bounces against you, and once your bounce rate passes about 2%, the working limit most sending platforms enforce, your messages start landing in spam even for real recipients.
Is it a valid address at all? The right shape, no stray spaces, a real top-level domain. This catches typos like "gmail.con". Free and instant.
The domain must publish an MX record, the internet's way of saying "send mail here". No MX means nothing can ever arrive. A domain with no mail server is a guaranteed bounce.
A verifier opens a conversation with the receiving server and asks whether the specific mailbox exists, then hangs up before any message is sent. A clear "no" means the address is dead.
Throwaway domains (the ones that expire in ten minutes) look real and accept mail, but the person is gone by tomorrow. A current disposable list flags these; see the disposable email checker.
Some servers accept mail for every possible address, so the mailbox check cannot tell a real address from a guess. These come back as "catch-all", which means unconfirmed, not valid. Full explanation: catch-all email checker.
Type the part after the @ into a browser. If there is no website and the company does not exist, the address almost certainly does not either.
Most companies use one format, such as first.last@. If you know one real address at the company, you can see whether the one you have fits the pattern.
Paste the address in quotes into a search engine. Real work addresses often appear in signatures, directories or press releases; invented ones do not.
The four signals above, run properly against the live mail server, in under a second. That is what the check below does, for one address or a whole list.
Two cases cannot be confirmed by any honest tool. A catch-all server accepts everything, so a guess passes the mailbox check. And some corporate and ISP gateways refuse the check entirely, which comes back as "unknown". Across business domains we verify, 27% return unknown for this reason. A tool that marks those "valid" is guessing; a tool that marks them "unknown" is telling you the truth and, in our case, not charging you for them.
Run it through a free verifier, which checks the syntax, the domain's mail records, and whether the mailbox answers, all without sending anything. BounceZero does this for 100 addresses a month at no cost. By hand, you can check that the domain has a working website and that the address fits the company's usual format, but only a mailbox check confirms it.
Yes, for most addresses. A verifier opens a connection to the receiving mail server and asks whether the mailbox exists, then closes it before any message is delivered. The recipient never sees anything. The exceptions are catch-all servers and gateways that block the check, which come back as unconfirmed rather than valid.
Two different things. A mistyped or invented address that no mailbox answers to, which a verifier catches as invalid. Or a disposable address on a throwaway domain that works today and is gone tomorrow, which a verifier flags as disposable. Both bounce or go nowhere if you mail them.
Because a well-formed address is not the same as a live mailbox. The person may have left, the mailbox may be full or deleted, or the address may sit on a catch-all server that accepted your guess and bounced it later. Verifying against the live server before you send is the only way to know.
Yes. A proper verification never sends a message, so there is nothing for the recipient to see and nothing that affects your sender reputation. It is the sending to unverified addresses that damages reputation, not the checking.
Paste one address or a whole list. Real, fake, disposable, catch-all and unknown, each labelled honestly. 100 checks a month at no cost, unknowns never charged.
Ayoub built BounceZero's 5-stage validation pipeline, its dedicated sending infrastructure, and the high-availability database behind every verification. Previously built high-volume email delivery systems. Trained at 1337 Benguerir (École 42 network, 2019). Open-source: bgp_analyzer.
Single-email checks, no signup required
Verifier, bounce calculator, header analyzer + more
Block temp-address signups at the source
Predict a bounce before sending
Syntax, MX, SMTP, catch-all and API explained
The cost of a check vs the cost of a bounce
Check if any email address is real
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