---
title: "Check Email Canonical"
method: POST
path: "/auth/check-email-canonical"
tags: ["domain-limit"]
---

# Check Email Canonical

`POST /auth/check-email-canonical`

Check whether a Gmail address is a dot-trick duplicate of an existing account.

Only meaningful for ``@gmail.com`` / ``@googlemail.com`` addresses.
Always returns ``duplicate: false`` for all other domains.
This intentionally trades limited account-enumeration exposure for a clear
signup error; the unauthenticated route is IP-rate-limited.

## Request body

- EmailCanonicalRequest — Request body for checking Gmail canonical duplicate status.
  - `email` string, email, required

## Response `200`

Successful Response

- EmailCanonicalResponse — Response describing whether a canonical Gmail duplicate exists.
  - `duplicate` boolean, required

## Other responses

- `422` — Validation Error

## Changes

- **2026-09-24** `1cffaad2a921` — 1 warning, 1 info
  - removed the optional property `detail` from the response with the `422` status
  - added the required property `error` to the response with the `422` status

[Change history](https://skmtc.dev/pioneer/apis/brain-api/changes/auth/check-email-canonical/post.md)

---

[API](https://skmtc.dev/pioneer/apis/brain-api.md) · [All operations](https://skmtc.dev/pioneer/apis/brain-api/llms.txt) · [OpenAPI document](https://skmtc.dev/pioneer/apis/brain-api/revisions/1cffaad2a921?raw)