Email Syntax Validator

Email Syntax Validator — Free RFC 5322 Format Checker

Paste or type any email address and instantly find out whether its format is valid. This tool checks syntax against RFC 5322 — the internet standard that defines how email addresses must be structured — entirely in your browser, with no data sent to any server.

Unlike paid email verification services that charge per credit to check whether a mailbox actually exists, this validator focuses on what you can know for free: whether the address is correctly formatted and free from typos that would make it undeliverable before a message even reaches a mail server.

How to Use the Email Format Checker

1. Type or paste an email address into the input field above.
2. Click "Validate Email" or press Enter — the result appears instantly.
3. Review the four criteria — Format Check, Domain Syntax, Real Provider, and TLD Check — to understand exactly what passed or failed.

The Address Metadata panel also breaks the address into its parts: local part, domain name, TLD, and a provider reputation score from 0 to 10.

What Makes an Email Address Valid? (RFC 5322)

A valid email address must satisfy all of the following criteria:

Local part (before the @):

• Contains only letters (a–z, A–Z), digits (0–9), and the special characters: + - _ . ! # $ & ' * / = ? ^ { | } ~
• Does not start or end with a dot (.)
• Does not contain two consecutive dots (..)
• Is between 1 and 64 characters long

@ symbol:

• Exactly one @, present and not at the start or end of the address

Domain (after the @):

• Contains only letters, digits, hyphens (-), and dots (.)
• Does not start or end with a hyphen or dot
• Does not contain two consecutive dots
• Each label (section between dots) is between 1 and 63 characters

Top-level domain (TLD):

• At least 2 characters (e.g., .com, .io, .br)
• Letters only — no digits or special characters

Common Email Validation Errors

Common Use Cases

• Form validation testing: QA engineers use this to test edge-case email inputs in registration forms, login flows, and API endpoints before a release. A single invalid example can expose gaps in back-end validation logic.
• Pre-send list hygiene: Email marketers paste addresses from imported lists to catch obvious syntax errors before uploading to a sending platform, reducing hard bounces and protecting sender reputation.
• Debugging validation rules: Back-end developers working on custom email validation in JavaScript, Python, or PHP can compare their regex output against this checker to spot discrepancies in their implementation.
• Learning RFC 5322: Students and developers new to email systems use this to interactively explore which formats are valid and why, making the abstract standard concrete.
• Catching copy-paste errors: Users who copied an email from a document or messaging app can verify it before entering it into a critical field — invisible trailing spaces are a surprisingly common culprit.

Frequently Asked Questions

What is the difference between an email validator and an email verifier?

An email validator checks whether an address is correctly formatted according to RFC 5322 — it verifies syntax only and does not connect to any server. An email verifier goes further: it checks whether the domain has working MX records and attempts an SMTP handshake with the mail server to confirm the mailbox actually exists and can receive messages. Validation is fast, free, and private. Verification requires a network request and is typically a paid service. Use a validator to catch typos and format errors; use a verifier before sending marketing campaigns.

What is RFC 5322 and why does it define valid email addresses?

RFC 5322 is the internet standard published by the IETF (Internet Engineering Task Force) that defines the format and syntax rules for email messages, including what constitutes a valid email address. It replaced the earlier RFC 2822 and RFC 822. Most email systems, programming languages, and validation libraries implement RFC 5322 (or a practical subset of it) as the authoritative definition of a well-formed email address. Following RFC 5322 ensures that your validation logic aligns with how real mail servers interpret and route email.

Can an email address be syntactically valid but not deliverable?

Yes. Syntax validation only checks format — it cannot determine whether a mailbox actually exists or whether the mail server is currently accepting messages. For example, anything@example.com is syntactically valid, but example.com is a reserved domain and will not deliver email. Similarly, an address might be correctly formatted but the mailbox could be inactive, over quota, or on a non-existent domain. For deliverability checks, a full email verification service that queries MX records and performs SMTP verification is required.

Is this email validator safe to use with real email addresses?

Yes. This validator runs entirely in your browser using JavaScript. The email address you enter is never transmitted to a server, stored in a database, or shared with any third party. The validation logic executes locally on your device. This makes it safe to use with real addresses, sensitive business contacts, or any data you would not want to send to an external service.

Why does my email seem valid but the system says it is invalid?

The most common causes are: an invisible space at the start or end of the address (common when copying and pasting), two consecutive dots, a special character like an accent or emoji in the local part, an unusual TLD the validator does not recognize, or a local part exceeding 64 characters. Try typing the address manually instead of pasting it to rule out hidden spaces.

Resources

• RFC 5322 — Internet Message Format (IETF) — The authoritative standard defining valid email address syntax, published by the Internet Engineering Task Force.
• MDN — HTML input type="email" — MDN's reference for the browser's built-in email validation behavior and its relationship to RFC 5322.