Free tool

Email syntax checker. See if an address is written correctly.

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

Trueguard Basic is free

Run the same check at scale.

Use it through the API to check signups, lead forms and email lists.

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No credit card required.

False positive rate<1%

Median responseSub-1s

Free here10 / day

With a free account100 / month

Check the format of an address.

10 free checks a day, no signup and no card. Nothing is sent to the address you check.

Or try

Typos at the form

A missing dot or a stray space means your welcome email never arrives, and the user never comes back.

Broken imports

Malformed rows in an imported list cause send errors and clutter every system the list reaches.

Cheaper at the source

Rejecting a bad format at entry costs one check. Finding it later costs a bounce, a support ticket, or a lost user.

How does the checker validate email syntax?

Deterministic first, then the same checks the full verifier runs.

Check the format against RFC 5322

A local part, an @ symbol, and a domain with a valid top-level domain. This step is deterministic: the same address always gets the same answer, and typos fail here.

Resolve the domain and MX records

Correct format does not mean the domain exists. We resolve it and read the mail servers it publishes, because a perfectly formatted address at a domain with no MX records still cannot receive mail.

Run the SMTP check and read the verdict

We open an SMTP handshake with the destination server and stop before sending. Format, domain and mailbox together produce one verdict instead of three separate guesses.

What each result means.

Every answer, in plain English.

safe

The format is correct, and the checks after it passed too: the domain has mail servers and the mailbox accepts mail.

risky

The format is correct and the address can receive mail, but it carries a flag, such as a throwaway domain or a shared inbox.

invalid

The address fails the format check, or it is written correctly but the domain or the mailbox cannot receive mail.

unknown

The format is correct, but the mail server did not confirm the mailbox. A correct format alone never proves an address works.

Three quick definitions.

What is RFC 5322?

The internet standard that defines the grammar of an email address: a local part, an @ symbol, and a domain. It is the reference every format check works from, which is why a syntax verdict is deterministic - the same address always gets the same answer.

What is the local part?

Everything before the @ symbol. It may contain letters, digits, and a limited set of punctuation, and it is case-sensitive in the standard even though almost no provider treats it that way in practice.

Is name+tag@gmail.com valid?

Yes. Sub-addressing with a plus sign is valid syntax and delivers to the base mailbox. We flag it as a sub-address so you can decide whether to treat aliases differently at signup.

When should you use the API instead of this page?

The API returns the same signals plus structured fields and 50,000 monthly validations on the paid plan. The free tier is 100 a month, no card.

One address, by hand

This page

A handful of leads from a CSV

This page, or the API with a 10-line script

Every signup, every form submit

Email validation API. Call it from your backend.

Hundreds of thousands a month

Email validation API, Standard plan

curl -X POST https://api.trueguard.io/v2/email/validation \
  -H "X-API-KEY: $YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"email":"name@example.com"}'

Read the API documentation

Questions about email format.

Still stuck? Contact support or read the documentation.

What counts as valid email syntax?

The RFC 5322 grammar: a local part, an @ symbol, and a domain with a valid top-level domain. Addresses with spaces, two @ symbols, a missing dot in the domain or trailing punctuation fail the format check.

Does valid syntax mean the address works?

No. Format only proves the address is written correctly. The domain may not exist and the mailbox may never have been created, which is why this checker also resolves MX records and runs an SMTP check.

Is name+tag@gmail.com valid?

Yes. Sub-addressing with a plus sign is valid syntax and delivers to the base mailbox. We flag it so you can decide whether to treat aliases differently at signup.

Are the format rules the same everywhere?

The RFC is, but mail providers add their own restrictions on length and characters. An address can be technically valid and still be rejected by the destination server, which the SMTP step catches.

Can I validate format in my own signup form?

Yes. The validation endpoint returns the syntax flag with every other signal in one call, 100 validations a month free, no card.

Validate format at the point of entry.

The same check runs through our validation endpoint. 100 free a month, no card. Same accuracy, same response shape, ready to drop into your backend.

Get your free API key

No credit card required.