---
title: "Internationalized email addresses"
description: "Accept and preserve Unicode mailbox addresses only when every validation, storage, SMTP, and support path handles SMTPUTF8 safely."
canonical: https://specification.email/spec/internationalisation/international-addresses/
category: internationalisation
status: recommended
sources:
  - title: "RFC 6531 — SMTP Extension for Internationalized Email"
    url: "https://www.rfc-editor.org/rfc/rfc6531"
    publisher: "IETF"
---

# Internationalized email addresses

> Accept and preserve Unicode mailbox addresses only when every validation, storage, SMTP, and support path handles SMTPUTF8 safely.

## What it is

SMTPUTF8 permits UTF-8 in mailbox local parts and extends SMTP negotiation for internationalized addresses and headers.

## Why it matters

ASCII-only validation excludes legitimate addresses, but partial support can accept an address that a later system cannot send to or display.

## How to implement

Preserve Unicode, validate syntax without inventing narrower rules, store sufficient length, negotiate SMTPUTF8, and use IDNA consistently for international domain names.

## Common mistakes

- Lowercasing or normalizing the local part destructively.
- Applying website-domain validation to a full mailbox.
- Advertising support while a bounce processor is ASCII-only.

## Verification

Run international-address fixtures through sign-up, database, API, queue, MTA, webhook, suppression, export, and support tooling.