Free Tool
Free Email Syntax Checker
An email syntax check confirms an address is formatted correctly before you rely on it. It validates the structure against the RFC 5322 standard: a local part, an @ symbol, and a domain with a valid top-level domain. This checker leads with the format verdict, then goes further with MX and SMTP checks. 10 checks per day, no signup.
Need to validate format on every signup or across a list? Use the API
Paste an address above. Or try one of the examples below.
What is an email syntax check?
An email syntax check confirms an address is written in a valid format. It validates the structure against the RFC 5322 standard: a local part, an @ symbol, and a domain that ends in a valid top-level domain. If any part is missing or malformed, the format is invalid. A syntax check is different from an existence or deliverability check. Correct formatting only proves the address could exist, not that the mailbox is real or that mail will arrive. This checker leads with the format verdict, then adds MX and SMTP checks for a fuller picture.
How do I check if an email format is valid?
To check an email format, enter the address in the field above. The checker returns the format verdict first, then confirms whether the domain is set up to receive mail and gives an honest deliverability status. It works on any domain, including Gmail, Outlook, and custom company domains.
The format verdict leads
The headline result is the format check. Address format is valid means the address matches the RFC 5322 structure: a local part, an @ symbol, and a domain with a valid top-level domain. Address format is invalid means a part is missing or malformed. This is the verdict you see first.
Domain and MX validity
A valid format is not enough on its own, so we resolve the domain and look up its MX records. Domain can receive mail confirms the domain has mail servers. A domain with no MX records cannot accept email at all, no matter how the address is spelled, so we flag that too.
Honest deliverability status
Alongside the format verdict you get a deliverability status: safe, risky, invalid, or unknown. A catch-all domain comes back risky, since it accepts mail at the server but cannot confirm the mailbox. Unknown means the mail server gave no clear answer. We never label a guess as safe.
How does the checker validate email syntax?
Validating syntax is the first step, and the checker does not stop there. It reads the address structure against RFC 5322, then resolves the domain and runs a live SMTP check. A regex on its own cannot tell you any of what comes after the format verdict.
Check the format against RFC 5322
First we parse the address against the RFC 5322 standard. We confirm there is a local part, a single @ symbol, and a domain that ends in a valid top-level domain. If the structure is wrong, the format is invalid and we say so. This is the verdict that leads the result.
Resolve the domain and MX records
A valid format does not mean the domain can receive mail, so next we resolve the domain and look up its MX records. Working MX records confirm the domain has mail servers and can accept email. No MX records means the address cannot receive mail, whatever its format. This is the prerequisite for the SMTP check.
Run the SMTP check and read the verdict
Finally we open an SMTP handshake with the mail server and read its response, without sending a message. The server's answer maps to the deliverability status: safe, risky, invalid, or unknown. A regex alone cannot do this. It can confirm format, but it cannot tell you whether mail will actually be accepted.
Why does email format validation matter?
A malformed address costs you every time it slips through. It bounces, it breaks your forms, and it pollutes your lists. Validating the format up front, then checking the domain and mailbox, keeps bad addresses out before they cause problems downstream.
Catch typos and malformed addresses at signup
People mistype their address or enter junk to skip verification. A format check catches gmial.com, a missing @, and a broken domain before the account is created. Pair it with disposable detection to catch throwaway addresses that are formatted correctly but exist only to get past your form.
Stop bounces and protect sender reputation
Every message to a malformed or dead address bounces, and a high bounce rate lowers your sender reputation with Gmail, Outlook, and Yahoo. Validating the format and confirming the domain can receive mail before you send keeps your bounce rate down and keeps your mail landing in the inbox.
Keep forms and lists clean
A single bad address in a list spreads downstream into your CRM, your analytics, and your billing. Checking the format at the point of entry stops invalid addresses before they are stored, so your lists stay clean and your team is not chasing addresses that were never valid to begin with.
An honest verdict, never a false valid
Some addresses are correctly formatted but cannot be confirmed at the mailbox, and we say so. We would rather flag an address risky or unknown than call a guess safe. An honest status tells you exactly how much to trust an address, which is more useful than a confident wrong answer.
What can a syntax check not tell you?
A syntax check has honest limits, and we surface them instead of hiding them. A valid format proves the address is written correctly. It does not prove the mailbox is real, that the domain can receive mail, or that your message will be delivered. That is why this checker goes past the format verdict and adds MX and SMTP checks.
Even then, two cases cannot return a clean result. A catch-all domain accepts mail for every possible address, real or not, so the SMTP response cannot confirm the specific mailbox. We flag these risky: deliverable at the server, unconfirmed at the mailbox. For a domain-level look, use the catch-all email checker.
Some mail servers block verification probes or give no clear answer. When that happens we return unknown rather than guess. To confirm a specific mailbox is real, use the email existence checker. For the full multi-signal check, use the email verifier.
What does email format validation cost at scale?
This tool is free for 10 checks a day, no signup. To validate format on every signup or across a full list, the same check ships in the email verification API. 100 validations a month free, no card, then $49.99 a month for 50,000.
Pay for what you check. Cancel anytime. Overage is billed through Stripe at $0.001 per validation regardless of volume.
What counts as a validation? One request to the validation endpoint is one validation. Failed calls (4xx from your side) do not count.
Frequently asked questions
What is an email syntax check?
An email syntax check confirms an address is written in a valid format. It validates the structure against the RFC 5322 standard: a local part, an @ symbol, and a domain that ends in a valid top-level domain. If a part is missing or malformed, the format is invalid. It does not prove the mailbox is real or that mail will be delivered.
How do I check if an email format is valid?
Enter the address in the checker above and read the verdict. The format result comes first: address format is valid or address format is invalid, based on the RFC 5322 structure. We then resolve the domain, check its MX records, and run an SMTP check, so you also get an honest deliverability status of safe, risky, invalid, or unknown.
What is RFC 5322 and why does it define a valid email?
RFC 5322 is the internet standard that defines how an email address is structured. It specifies the local part before the @ symbol, the @ symbol itself, and the domain after it, ending in a valid top-level domain. It is the agreed-upon rule for what counts as a correctly formatted address, so a syntax check measures an address against it.
What makes an email address an invalid format?
An address is an invalid format when it breaks the RFC 5322 structure. Common causes are a missing or duplicate @ symbol, no domain, a domain with no valid top-level domain, spaces, or illegal characters in the local part. A typo like gmial.com is still a valid format, since the structure is correct even when the domain is wrong.
Is a syntactically valid email always a real, deliverable address?
No. A valid format only proves the address is written correctly. The mailbox may not exist, the domain may not accept mail, and the server may still reject your message. That is why this checker goes past the format verdict and adds MX and SMTP checks. To confirm a specific mailbox, use the existence checker.
Why is a regex not enough to validate an email address?
A regex can only check the format, and even then a correct RFC 5322 pattern is hard to get right. It cannot resolve the domain, look up MX records, or run an SMTP check, so it cannot tell you whether the domain accepts mail or the mailbox exists. Format is the first step, not the whole answer.
Is this email syntax checker free?
Yes. 10 checks per day, no signup, no card, no email required. The check is ReCaptcha protected. If you need more, a free Trueguard account lifts you to 100 validations a month through the API, and the paid plan covers 50,000.
Is there an API to validate email format at scale?
Yes. The same check runs in the Trueguard email verification API at POST /email/validation. It returns the format verdict and deliverability status as structured fields you can act on in your backend. 100 free validations a month, then $49.99 a month for 50,000.
