Email checker that tells you the truth

This free email verifier checks any email address, or a whole pasted list, for syntax errors, a working mail server (MX), SPF and DMARC. It runs in your browser, so nothing is uploaded. What it cannot do: confirm a mailbox exists. Only a server-side SMTP probe or a real send can do that.

Paste email addresses

One address per line. Pasted CSV rows work too: we pull the address out of each line.

0 lines pasted

Nothing leaves your browser except DNS queries for each unique domain, sent to Google's public DNS resolver. Your addresses are never sent anywhere.

Read this before you trust any result. A browser cannot open an SMTP connection, so no tool that runs in your browser can confirm that a mailbox exists. This checks syntax, DNS and reputation signals. That catches most of the bad rows on a typical list, and it will never tell you "this mailbox is real".

Working

Results, annotated

Every row carries the reason for its verdict, the mail host we found and the domain's SPF and DMARC state.

Domains in this list

One DNS lookup per unique domain, cached for the whole session. Five hundred addresses on one domain cost one lookup, not five hundred.

Your list is checked

Syntax and DNS are the cheap half. The other half is sending from a domain that authenticates, at a volume that does not burn it.

Send with Overloop

What each verification method actually proves

Every email verification tool sits somewhere on this ladder. Tools sell the top rungs and quietly deliver the bottom ones, so here is the whole ladder with what each rung proves and what it costs.

Method	What it proves	What it cannot prove	Cost
Syntax check this tool	The address is a well formed address under RFC 5321 and RFC 5322 length and character rules.	Anything at all about the domain or the mailbox. A perfectly formed address can point nowhere.	Free, instant, works offline
MX and DNS lookup this tool	The domain exists, runs a mail server, and which provider hosts it. SPF and DMARC presence at the domain.	Whether the specific mailbox behind that server exists, or whether it is still in use.	Free, instant, one lookup per domain
List hygiene flags this tool	Disposable domains, role accounts, free providers, and typos in common domains with the correction.	Whether a flagged address is genuinely worth removing. That is a judgement call about your offer.	Free, instant, no lookup needed
SMTP probe (RCPT TO)	The receiving server's own answer for that one mailbox, at that one moment, when it answers honestly.	Nothing on a catch-all domain, which accepts every address. Many providers also refuse to answer probes or answer 250 for addresses that do not exist.	Paid, priced per address. Needs a server, not a browser.
Catch-all detection	Whether the domain accepts mail for addresses that were never created, which tells you the SMTP probe is meaningless there.	Which mailboxes on that domain are real. On a catch-all domain, no verifier can tell you.	Paid, usually bundled with the SMTP probe
A real send	Everything. A hard bounce or a delivery is the only definitive answer that exists.	Nothing. This is the ceiling. It is also the one method that costs you something you cannot buy back.	Free to run, paid for in sender reputation

Bounce rate targets to keep in mind: Google and Yahoo both publish sender guidance that treats a spam complaint rate at or above 0.3 percent as a problem, and mailbox providers weigh repeated hard bounces the same way. Cleaning syntax and DNS failures before you send removes the cheapest source of both.

Why a browser cannot verify a mailbox, and who says otherwise

Verifying that a mailbox exists means opening a TCP connection to the receiving mail server on port 25, saying HELO, then MAIL FROM, then RCPT TO, and reading the response code. JavaScript in a browser tab cannot open a raw TCP socket. There is no flag, no permission prompt and no clever workaround. Any tool whose verification happens entirely in your browser stops where this one stops.

So when a free web tool tells you an address is "valid" or shows you a green tick per address, one of three things is true. It runs the SMTP probe on its own server and is not free at scale. It checks syntax and DNS and calls that "valid", which is what this page refuses to do. Or it guesses.

Even a real SMTP probe is not a guarantee

Catch-all domains accept everything. If a domain is configured to accept mail for any address, RCPT TO returns 250 for a mailbox that was never created. A large share of company domains are configured this way.
Microsoft 365 tenants often refuse to answer. Depending on how directory based edge blocking is set, a tenant can accept every recipient at the edge and reject internally after the connection closes, which no probe can see.
Greylisting and rate limits distort the answer. A temporary 4xx says nothing about the mailbox, and a probe that treats it as a failure will delete good addresses from your list.
Probing burns the IP you probe from. Repeated RCPT TO from one IP with no message is a well known abuse pattern. This is why credible verification providers charge for it.

The practical answer is a sequence, not a single tool. Strip syntax and DNS failures for free with this email checker. Pay for an SMTP probe only on what survives, and only when the list is large enough to matter. Then let real sends give you the last, definitive answer, on small batches first so a bad segment cannot take your domain down with it. If you would rather have the whole sequence run inside one workflow, that is what Overloop's email verification does before a campaign goes out.

How to verify an email address, or ten thousand

Paste

One address, a column pasted out of a spreadsheet, or a few thousand rows of CSV. We pull the address out of each line.

Verify

Syntax per address, then one cached DNS lookup per unique domain for MX, SPF and DMARC. Progress is shown as it runs.

Export

Read the annotated table, copy the addresses that passed, or export every row with its reason to CSV.

What we flag, and why it matters for outreach

Invalid syntax with the specific rule that failed, not just a red cross. Two dots in a row, a local part over 64 characters, a hyphen at the edge of a domain label, a numeric top-level domain.
No mail server. The domain resolves but has no MX record, or publishes a null MX (a single MX of 0 .), which is the domain owner explicitly saying it accepts no mail. Both bounce, every time.
Likely typo in a common domain, with the correction. gmial.com, hotmial.com, yahooo.com and a TLD ending in .con or .cmo are the four that show up on almost every list.
Disposable or throwaway domains. A signup from mailinator.com or a ten minute mail service is not a prospect and will never reply.
Role accounts. info@, sales@, support@, admin@ and no-reply@ reach a shared inbox or nothing. They also attract complaints faster than personal addresses, and some of them (abuse@, postmaster@) are monitored specifically for that.
Free providers. Not a fault, but on a B2B list a gmail.com address usually means you enriched the wrong person, or someone gave you a personal address to avoid you.
Missing SPF or DMARC on the receiving domain, which tells you how strictly that domain's own provider is likely to be filtering what you send it.

Already have the address and want to know who is behind it, or have the person and need the address? Use the reverse email lookup to go from an address to a person, and the email finder to go the other way. Verify whatever comes out of either one here before you send to it.

Questions we get every day

Paste it into the box above and press Verify list. The tool checks the syntax against RFC 5321 and RFC 5322 rules, then looks up the domain's MX, SPF and DMARC records over DNS. That tells you for free whether the address is well formed and whether the domain can receive mail at all, which is what removes most bad rows from a list. It cannot tell you the mailbox exists, and no free browser tool can.

No. Confirming a mailbox means opening a TCP connection to the mail server on port 25 and reading the answer to an SMTP RCPT TO command. Browsers cannot open raw TCP sockets, so this is a hard limit, not a missing feature. Only a server-side SMTP probe or an actual send can answer that question, and even a probe is defeated by catch-all domains.

A few thousand in one paste, comfortably. The limit in practice is DNS, not the addresses: lookups are done once per unique domain and cached, so a list of five thousand addresses across forty domains finishes in seconds, while five thousand addresses across five thousand different domains takes minutes. The table shows the first two hundred rows to keep the page responsive, and the CSV export always contains every row.

No. The addresses stay in the page. The only network requests are DNS queries for each unique domain, sent to Google's public DNS-over-HTTPS resolver, and a domain name is not personal data in the way an address list is. There is no account, no server of ours in the path, and nothing is stored after you close the tab.

A null MX is a single MX record with priority 0 pointing at the root, written as 0 . It is defined in RFC 7505 and it means the domain owner has explicitly declared that this domain accepts no email. example.com publishes one. Anything you send to a null MX domain bounces immediately, so those rows are safe to delete without paying anyone to check them.

For cold outreach, usually yes. A role account reaches a shared inbox, a ticketing system or nobody, and complaints from shared inboxes count against your sending reputation the same as any other. Some role addresses exist specifically to receive reports about senders: abuse@ and postmaster@ are required by RFC 2142 and mailing them cold is a bad idea. For support or billing follow-ups, role accounts are exactly right.

Because a passing verdict here means the domain can receive mail, not that the mailbox exists. The person left the company, the alias was retired, the mailbox is full, or the domain is a catch-all that accepts everything and drops what it does not recognise. This is the gap that only an SMTP probe or a real send closes, which is why the verdict on every row says the domain passed rather than the address is valid.

Yes. No account, no credit limit, no per-address charge, and no cap on how many times you run it. It costs us nothing to run because the work happens in your browser. The paid product is what comes after a clean list: sending, sequencing and reply handling.

More free tools

Clean list. Now send it.

Overloop verifies, sequences and sends, then tells you who replied. First campaign live in 15 minutes.

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Email checker that tells you the truth

Results, annotated

Domains in this list

Your list is checked

What each verification method actually proves

Why a browser cannot verify a mailbox, and who says otherwise

Even a real SMTP probe is not a guarantee

How to verify an email address, or ten thousand

Paste

Verify

Export

What we flag, and why it matters for outreach

Questions we get every day

More free tools

Email finder

Reverse email lookup

Domain health checker

Spam checker

Clean list. Now send it.