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Email Syntax Checker

Test an address against the RFC rules, rule by rule.

Email Validator Tools Reviews Free · no sign-up

Quick Tool Overview

The Email Syntax Checker walks an address rule by rule against RFC 5322 and 5321 — characters, quoting, dots, hyphens, labels and every length limit — and names the rule that fails.

What it does
Tests an address against each RFC syntax rule separately
You give it
One email address
You get back
A rule-by-rule result and a parts breakdown
Standards covered
RFC 5322 syntax and RFC 5321 length limits
Best for
Settling whether a form is right to reject an address
Email Validator Tools Free, unlimited use No sign-up Runs in your browser

About the Email Syntax Checker

A syntax checker that shows its working. Instead of one pass or fail, it walks the address rule by rule: the characters the local part may hold unquoted, whether a quoted form is balanced, leading and trailing dots, consecutive dots, the 64-character local limit, then the domain labels, their length, their hyphens, the top-level domain and the 254-character total.

That makes it useful for the argument you are actually having — whether a form is right to reject an address. A surprising amount of perfectly legal syntax gets refused by validation regexes written from memory: plus signs, apostrophes, single-character local parts, long new TLDs and international domains all trip them up.

Every rule cites what it is testing, so you can take the result to whoever wrote the regex.

Key features of the Email Syntax Checker

Rule by rule, not pass or fail

Each check names what it tested and what it found.

Legal but risky syntax flagged

Quoted local parts and IP literals get a warning, not a cross.

Parts breakdown

Local part, domain, each label and the TLD shown separately.

Catches over-strict regexes

Plus signs, apostrophes and long TLDs are correctly accepted.

Runs offline

Nothing you paste is sent anywhere.

How to use the Email Syntax Checker

  1. 1

    Paste the address

    The one a form accepted or rejected that you want to settle.

  2. 2

    Read the rule list

    Each RFC rule is listed with a tick, a warning or a cross.

  3. 3

    Check the breakdown

    The local part, domain, labels and TLD are shown separately.

  4. 4

    Note the warnings

    A warning is legal syntax that many systems reject anyway.

Frequently asked questions

Yes. The plus sign is in the RFC 5322 atext set and is perfectly legal in a local part. Most providers also treat what follows it as a routing tag, which is a separate convention on top of the syntax.

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