The correct strategy is to use all available identifiers to build the most complete view of the customer. In XDM, this is achieved by populating an identityMap field for each record. This map contains all known identifiers for the customer (CRM ID, email, mobile number) under their respective namespaces. The Adobe Experience Platform Identity Service then processes this map to link, or "stitch," these identifiers together into a single identity graph, enabling robust profile merging and segmentation.

A. Ignoring available identifiers like email and mobile number would result in fragmented profiles and an incomplete customer view, defeating the purpose of a CDP.

C. While one identifier is marked as "primary" in a schema for ingestion purposes, all identifiers in the identity map are used for stitching. This option oversimplifies the process.

1. Adobe Experience Platform Documentation. (2023). Identity Service overview. Adobe Experience League. Retrieved from https://experienceleague.adobe.com/docs/experience-platform/identity/home.html?lang=en. This document describes how Identity Service uses identity maps to link identities.

2. Adobe Experience Platform Documentation. (2023). Troubleshooting guide for Identity Service. Adobe Experience League. Retrieved from https://experienceleague.adobe.com/docs/experience-platform/identity/troubleshooting.html?lang=en#unstitched-identities. This guide implicitly shows how multiple identities (e.g., ECID and CRM ID) are expected to be present in an identity map to be stitched.