Email validation
Email validation that admits what it cannot know
Mail7 checks the syntax, the domain's mail servers, then the mailbox itself, and answers Valid, Not Valid or Unknown. Unknown means the mail server would not say, not that the address is bad.
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Syntax
Well formed, single mailbox
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Mail servers
outlook-com.olc.protection.outlook.com
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Mailbox
Server accepts every recipient, so it proves nothing
Unknown, and that is the true answer. Microsoft will not confirm whether this mailbox exists. Another service would print "Valid" here and let you find out at send time.
The third answer
Two answers are easy. The honest number is three.
Whether a mailbox exists is decided by the receiving mail server. Plenty of them, including Microsoft, Yahoo, catch-all domains and anything behind greylisting, deliberately refuse to say. A verdict of Valid or Not Valid in those cases is a guess with a confident face on it.
The server confirmed this mailbox exists and accepts mail. Send with confidence.
Broken syntax, no mail server for the domain, a disposable domain, or the server said the mailbox does not exist.
We could not get a straight yes or no. The address may be perfectly good. Treat Unknown as "no data", not as "bad address": keep it, and let engagement decide.
You are never billed for an Unknown result
Inside a check
Four stages, and the server's own words
Each stage can end the check on its own. Nothing is inferred from the ones before it, and nothing is filled in with a guess.
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01 · Syntax
The shape of the address
Local part, domain, length and characters, against the actual RFC rules rather than a regular expression someone found online.
ok local=j.pearce domain=outlook.com
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02 · Mail servers
Can the domain receive mail
We resolve the MX records. A domain without them cannot accept mail at all, whatever the address looks like.
MX 10 outlook-com.olc.protection.outlook.com
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03 · Mailbox
Ask the server about this one address
A real SMTP conversation, opened and closed without sending anything. The recipient never gets a message from us.
250 accepts all recipients (catch-all)
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04 · Verdict
One of three, never a fourth
If stage three produced proof, you get Valid or Not Valid. If it did not, you get Unknown and the reason why.
status = "Unknown"
Beyond one address
Clean the list, then fix the domain that sends to it
Bulk email checker
Paste a list or drop a CSV, pick the column with the addresses, and watch the verdicts land. Up to 1,000 addresses per run, exported back to CSV.
| Address | Verdict | Reason |
|---|---|---|
| [email protected] | Valid | Mailbox confirmed |
| [email protected] | Valid | Mailbox confirmed |
| [email protected] | Unknown | Server hides recipients |
| [email protected] | Not Valid | No mail server |
| [email protected] | Not Valid | Disposable domain |
1,000 rows · 2 min · CSV out
Check a listDomain checker
Your own domain decides whether your mail is trusted. One report covers MX, SPF, DKIM, DMARC, MTA-STS, TLS-RPT, DNSSEC and BIMI, with the fix for each problem.
lumen-labs.io
5 ok · 2 warnings · 1 problem
- SPF ends with -all
- DKIM 2048-bit key found
- DMARC p=none, nothing enforced
- MTA-STS not published
For developers
The same three answers, over HTTP
One POST, one JSON body, one honest status. Ready-made pieces for WordPress, Zapier, n8n, Make, Google Sheets, MailWizz and an MCP server for AI assistants.
curl -X POST https://mail7.net/api/validate-single \ -H "X-API-Key: mk_live_..." \ -d '{"email":"[email protected]"}' { "email": "[email protected]", "formatValid": true, "mxValid": true, "smtpValid": false, "status": "Unknown", "smtp_message": "Domain is catch-all" }
Reading a result
Understanding your results
Every address comes back with one of three clear statuses. We tell you exactly what we found and, just as importantly, when we cannot be sure.
- Valid
- The mailbox exists and can receive email. The mail server confirmed the address during our SMTP check.
- Not Valid
- The address cannot receive email: invalid format, no mail server (MX) for the domain, a disposable domain, or the server confirmed the mailbox does not exist.
- Unknown
- We could not get a definitive answer. Some providers (e.g. Outlook/Microsoft, Yahoo), greylisting, catch-all domains and anti-spam protections deliberately hide whether a mailbox exists. We report Unknown honestly instead of guessing.
Marks, not statuses
Two notes that travel with a result
Neither is a verdict of its own. They sit next to one of the three answers and tell you where the address came from.
- Disposable
- The domain is a temporary, throwaway mail provider. Such addresses are reported as Not Valid: they may work today, but not for lasting communication.
- Duplicate
- The same address appears more than once in an uploaded list. It is checked once and carries the verdict of its first occurrence. Duplicates in a file are never charged.
No service can verify every email with 100% certainty. Mailbox existence is controlled by the receiving mail server, and many providers intentionally do not reveal it to protect against spam and address harvesting. That is why some addresses are honestly marked Unknown rather than being forced into a Valid or Not Valid answer. We never guess: a clear result you can trust is more valuable than a confident-looking one that might be wrong.
Where it earns its keep
When to validate
Email validation is the process of confirming that an email address is valid, active, and can receive messages. It matters most at the moments where a bad address costs you something.
Before a campaign
Clean the list before you send. Fewer bounces, a protected sender reputation, and no budget spent mailing addresses that died in 2019.
At sign-up
Catch typos and disposable domains while the person is still on the form, when a correction costs one keystroke instead of a support ticket.
On imported leads
Lists bought, scraped or handed over at an event age fast. Verify before your sales team spends a week emailing nobody.
Inside your product
Call the API from registration, contact forms and data imports, and keep the database clean instead of cleaning it later.
Benefits of email validation
- Improve email deliverability rates
- Reduce bounce rates and spam complaints
- Protect sender reputation
- Save costs on email campaigns
- Better engagement with valid recipients
What we find in a typical list
- Typos in the domain: gmial.com, hotmial.com
- Domains that no longer accept mail at all
- Disposable addresses from sign-up forms
- Catch-all domains that accept anything
- Providers that block verification probes
Questions
Frequently asked questions
Ten answers about what a check can and cannot prove.
What is email checker?
An email checker is a tool that validates email addresses to determine if they are valid and deliverable. Our email checker performs multiple checks including format validation, MX records verification, and SMTP connection testing to ensure email addresses actually exist.
How to verify if an email address is valid?
To verify if an email address is valid, use our free email checker tool. Simply enter the email address and our system will check the format, verify MX records exist, and test SMTP connectivity to confirm the email address is deliverable.
Can you verify any email with 100% certainty?
No - and no email verification service can. Whether a mailbox exists is decided by the receiving mail server, and many major providers (such as Outlook/Microsoft and Yahoo), catch-all domains, greylisting and anti-spam protections deliberately do not reveal it to prevent spam and address harvesting. In those cases we honestly return the status "Unknown" instead of guessing. For most common providers and business domains, however, results are reliable.
What does the "Unknown" result mean?
"Unknown" means we could not get a definitive yes or no from the mail server. The address may well be valid, but the server did not confirm it - for example because of greylisting, a catch-all configuration, or an anti-spam policy that blocks verification probes. We prefer to tell you the truth ("Unknown") rather than report a Valid or Not Valid result we are not sure about.
Why did a valid email show as "Unknown"?
Some mail servers accept mail for every address (catch-all), delay unknown senders (greylisting), or block verification attempts based on the sender's IP reputation. When that happens we cannot confirm the specific mailbox, so a real, working address may be marked "Unknown". This is a limitation of how those servers are configured, not an error in the check.
What is a catch-all (accept-all) address?
A catch-all domain is configured to accept email sent to any address at that domain, even ones that do not exist. Because the server says "yes" to everything, we cannot tell whether a specific mailbox is real - so such addresses are reported as "Unknown" rather than falsely marked Valid.
How to check if an email is valid?
Check if an email is valid by using our email validator tool. Our email checker performs comprehensive validation including syntax checking, domain verification, and server connectivity testing to ensure the email address exists and can receive messages.
How to check bulk email is valid or not?
To check if bulk emails are valid, use our bulk email checker tool. You can upload a file with multiple email addresses or paste them directly. Our bulk email validator will process up to 1000 emails at once and provide detailed results for each address.
What are the benefits of email validation?
Email validation helps improve deliverability rates, reduce bounce rates, protect sender reputation, save costs on email campaigns, ensure compliance with regulations, and achieve better engagement with valid recipients.
Is email validation free?
Single email checks are free and need no account. Bulk checks are free with a free account: up to 1,000 addresses per file and 1,000 verified addresses a month, and Unknown results are never counted. API access is included on every plan, the Free one too - it just needs a confirmed email address. Paid plans add monthly volume and a higher request rate.
Start with one address. Bring the list when you trust the answers.
No account needed for single checks. 1,000 verified addresses a month on the free plan, and Unknown results never count against it.