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Email Length Validator

Measure an address against the RFC character limits.

Email Validator Tools Reviews Free · no sign-up

Quick Tool Overview

The Email Length Validator measures an address against all three RFC limits — 64 characters before the @, 253 for the domain, 63 per label and 254 overall — and shows the headroom left on each.

What it does
Measures an address against every RFC length limit
You give it
One email address
You get back
Each limit as a bar, with characters remaining
The limits
64 local, 63 per label, 253 domain, 254 total
Best for
Sizing a database column and validating long addresses
Email Validator Tools Free, unlimited use No sign-up Runs in your browser

About the Email Length Validator

The one question that comes up every time someone sizes a database column: how long can an email address be? The answer is three separate limits, and this measures an address against all of them — 64 characters for the local part from RFC 5321, 253 for the domain name, 63 for each individual label inside it, and 254 for the whole address in an SMTP reverse path.

Each is shown as a bar against its limit, with the number of characters left, so you can see which one an address is close to rather than only whether it passed. Internationalised domains are measured in their encoded form, because that is the one the limit applies to.

There is a note on the column width to use as well, which is the reason most people arrive here: 254 characters is the right size, and the 255 you will see everywhere is off by one for a reason that no longer applies.

Key features of the Email Length Validator

All four limits at once

Local part, each label, the domain and the whole address.

Headroom shown

How many characters are left before each limit, not just pass or fail.

Encoded length for IDN

International domains measured in their punycode form.

Column-width guidance

Settles the 254-versus-255 question with the reason behind it.

Instant and offline

Recalculates as you type, nothing sent anywhere.

How to use the Email Length Validator

  1. 1

    Paste the address

    Or the longest one you expect your system to see.

  2. 2

    Read each limit

    Local part, domain, each label and the total, measured separately.

  3. 3

    Check the headroom

    Each bar shows how many characters are left before the limit.

  4. 4

    Size your column

    The note at the bottom gives the width to store an address in.

Frequently asked questions

254 characters. The local part before the @ is capped at 64 and the domain at 253, but the practical overall maximum is the 254-character reverse path limit in RFC 5321.

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