# E17002 — MailboxHandleTaken

This handle is already taken. Choose a different handle.

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

## What to do

Handles are first-come, first-served and stay reserved once claimed. Choose a different handle for your mailbox.

## Related

- [Idempotency](/docs/api/idempotency): safe retries and key reuse rules
- [E17xxx — Agent mailboxes](/docs/api/errors/E17xxx): 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`