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Free tool

Email Syntax Checker

Check whether an email address is correctly formed, using the exact syntax rules of the RocketVerifier engine. Catch mistyped domains like gmial.com, or paste up to 500 addresses at once. Nothing leaves your browser.

Check

Uses the same syntax rules as the RocketVerifier engine. Everything runs in your browser: no address is sent to a server.

What the email syntax checker does

An email syntax checker tests whether an address is correctly formed before anything else is checked: one @, a local part of 64 characters or fewer, no consecutive or edge dots, a domain with a TLD, and 254 characters at most. This tool runs the checks and messages of the RocketVerifier engine in your browser and flags common domain typos such as gmial.com or hotmail.con.

How it works

How the Email Syntax Checker works

  1. Paste one or many

    Check a single address, or switch to Bulk and paste up to 500, one per line. Nothing leaves your browser.

  2. Same rules as our engine

    Length limits, the @, dots, the TLD and allowed characters are checked in the order the RocketVerifier engine uses, with the same messages.

  3. Fix typos, copy the rest

    Accept the suggested fix for a mistyped domain, then copy the valid addresses into a full verification.

Reading your result

What the result means

  • Valid syntax

    The address is correctly formed. It can still bounce: the domain, its MX records and the mailbox are checked in a full verification.

  • Invalid syntax

    The address breaks a format rule and cannot receive mail as written. A RocketVerifier verification returns it as undeliverable with the invalid_syntax sub-status.

  • Possible typo

    The domain looks like a misspelling of a popular mailbox provider, such as gmial.com for gmail.com. A full verification returns it as risky with possible_typo and the fix in did_you_mean.

  • Internationalised domain

    Domains such as bücher.de are valid. They are converted to their ASCII form (xn--bcher-kva.de), which is what mail servers receive.

Validation vs verification What is email validation? How SMTP verification works

Where syntax fits in a full verification

Syntax is the first of 7 checks every address goes through in RocketVerifier. An address that fails it stops here.

  1. 1

    SyntaxThis tool

    RFC-compliant format, typo detection and internationalised domains.

  2. 2

    Domain and DNS

    The domain exists and resolves.

  3. 3

    MX records

    The domain is set up to receive mail.

  4. 4

    Disposable and role

    Throwaway domains and shared inboxes such as info@ and sales@.

  5. 5

    Catch-all analysis

    Accept-all servers get a verdict: send safe, send with caution or avoid.

  6. 6

    SMTP mailbox check

    A live handshake confirms the mailbox exists, without sending an email.

  7. 7

    Risk signals

    Spam-trap patterns, toxic and do-not-mail addresses, and a 0 to 100 score.

FAQ

Email syntax checker FAQ

What makes an email address valid?

One @ sign, a local part (before the @) of 64 characters or fewer, a domain with at least one dot and a TLD, no consecutive dots, no dot at the start or end of the local part, and 254 characters or fewer in total. Letters, digits and the symbols !#$%&'*+/=?^_`{|}~.- are allowed before the @.

Does valid syntax mean the email address exists?

No. Syntax is the first of 7 checks in a RocketVerifier verification. The others confirm the domain resolves, it has MX records, it is not disposable or a role inbox, how a catch-all domain behaves, whether the mailbox exists through a live SMTP handshake that sends no email, and risk signals such as spam-trap patterns. Together they deliver 99.5% accuracy.

Why are quoted addresses like "john smith"@example.com rejected?

The full RFC 5322 grammar allows quoted local parts and comments, but mailbox providers do not issue addresses like that and most signup forms refuse them. Our engine follows the practical RFC 5321 subset that real mailboxes use. Non-ASCII local parts are rejected for the same reason: most receiving servers do not support them.

How are typos detected?

The checker uses the same curated list as our engine: common misspellings of Gmail, Outlook, Hotmail, Yahoo, iCloud and large ISP domains (gmial.com, hotmial.com, yahooo.com), plus wrong endings such as .con or .cmo on popular mailbox domains. In a full verification the engine also suggests close matches for domains that have no MX record.

Are the addresses I paste sent anywhere?

No. The rules run as JavaScript in your browser, so the addresses never reach our servers or anyone else. You can disconnect from the internet after the page loads and the checker keeps working.

Keep going

More free email tools

Syntax is check one. Run all 7.

A RocketVerifier verification adds DNS, MX, disposable and role screening, catch-all analysis and a live SMTP mailbox check, with 99.5% accuracy. Unknown results are never charged.

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100 free credits · No card required · Credits never expire