# E05011 — DomainHostnameReserved

This hostname is already in use as a return-path or tracking domain. Remove that configuration first, or choose a different domain.

- **HTTP status**: `409`
- **Type**: `conflict_error`
- **Name**: `DomainHostnameReserved`

## What to do

Remove the return-path or tracking configuration that uses this hostname, or choose a different domain, then retry.

Operations that resolve this:

- [List sending domains](/docs/api/reference/list-domains)
- [Update a sending domain](/docs/api/reference/update-domain)

## Related

- [Idempotency](/docs/api/idempotency): safe retries and key reuse rules
- [E05xxx — Domains & DNS](/docs/api/errors/E05xxx): every code in this range
- [Errors](/docs/api/errors): the full wire contract, status mapping, and error catalog
- [Error handling](/docs/guides/errors): branching on `type` and `code`, validation details, and `vendor_code`