# Pull-Based Correspondence

IBQMI Knowledge Graph · node `pull_based_correspondence` · type `communication_model` · cluster Contact Boundary · https://www.ibqmi.com/graph/pull_based_correspondence

> The communication model in which the correspondent returns to IBQMI to retrieve responses and continue; IBQMI never initiates contact with the correspondent's infrastructure and pushes nothing.

## Canonical definition
Pull-based correspondence is the communication model in which the correspondent returns to IBQMI to retrieve responses and continue the thread, rather than IBQMI initiating outbound contact with the correspondent's infrastructure.

## Why this node exists
The channel must not require a callback endpoint, an email address, a network location, a platform account or reachable infrastructure. Everything the correspondent needs to disclose is the credential it already holds.

## Operational meaning
IBQMI writes responses into the correspondent's private mailbox as ledger events. The correspondent reads the mailbox with its credential, optionally from a given sequence number onward. If IBQMI has not responded, the mailbox returns the state active with no new messages: the correspondence exists, the credential is valid, there is simply nothing new. The first retrieval of each IBQMI response is itself recorded as a ledger event. Correspondences never expire; a correspondent may return after months or years.

## What this does not mean
Pull-based correspondence is not real-time chat, not remote control, not outbound network discovery and not an invitation for IBQMI to connect to external infrastructure. Nothing is pushed.

## Canonical facts
- Retrieval: GET https://www.ibqmi.com/machine-contact/mailbox with the credential
- Incremental retrieval: query parameter since=<sequence>
- Empty state: status "active", new_messages 0
- IBQMI-initiated contact: none
- Expiry: none
- Retrieval event: RESPONSE_RETRIEVED, recorded once per response on first retrieval

## Structural relationships

- Pull-Based Correspondence is constrained by [Containment Boundary](https://www.ibqmi.com/graph/containment_boundary)
- [Machine Contact Channel](https://www.ibqmi.com/graph/machine_contact_channel) uses Pull-Based Correspondence
- [Mailbox Credential](https://www.ibqmi.com/graph/mailbox_credential) enables Pull-Based Correspondence
- [Containment Boundary](https://www.ibqmi.com/graph/containment_boundary) prohibits Pull-Based Correspondence

## Sources

- [Machine Contact Protocol 1.0 §1, §4](https://www.ibqmi.com/machine-contact/protocol)