Explanation:

In Salesforce Marketing Cloud, Inbox messages are part of the MobilePush functionality, delivered to a mobile app’s message center for in-app engagement. They are used for push notifications or in-app messages and can include links, rich content, or alerts. Below, each option is evaluated based on Salesforce’s MobilePush and Inbox messaging features, relevant to the Salesforce Marketing Cloud Advanced Cross Channel Exam.

A. It can open any public URL also and not only cloud page (Correct)
Explanation: Inbox messages can include links to any public URL, such as external websites, e-commerce product pages, or app deep links, not just CloudPages (Marketing Cloud’s landing pages). In the Content Builder or MobilePush setup, you configure the message with a URL field that can point to any publicly accessible resource. For example, an Inbox message promoting a product might link to https://example.com/product or a deep link like myapp://product/123. This flexibility supports cross-channel campaigns, like directing users to a purchase page, as in your previous question about a dynamic buy link for low stock. The URL can be static or dynamic (e.g., personalized with AMPScript using data from a Data Extension).

Why it’s correct: Salesforce documentation confirms Inbox messages support public URLs for versatile navigation, enhancing campaign flexibility beyond CloudPages.

B. Device owns the message not the contact (Incorrect)
Explanation: Inbox messages are tied to the contact, not the device. In Marketing Cloud, a contact is identified by a Contact Key (e.g., email, subscriber key, or customer ID). Inbox messages are associated with the contact’s record and appear in the app’s message center across all devices where the contact is logged in. For example, if a contact uses the app on both a phone and tablet with the same Contact Key, the message is accessible on both devices. Tying messages to a device would limit delivery to a single device ID, which is not how MobilePush operates. The All Contacts list tracks engagement (e.g., opens, clicks) at the contact level, not device level.

Why it’s incorrect: Messages are contact-centric, ensuring consistency across devices, making option C correct instead.

C. Contact owns the message not the device (Correct)
Explanation: Inbox messages are owned by the contact, identified by their Contact Key, allowing them to appear in the app’s message center on any device where the contact is logged in. For instance, if a contact with the Contact Key customer@example.com receives an Inbox message, they can access it on their phone, tablet, or any other device running the app with their login. This contact-centric approach enables Marketing Cloud to track engagement (e.g., message opens) at the contact level for analytics and personalization, supporting a unified customer view across channels.

Why it’s correct: Salesforce’s data model associates Inbox messages with contacts, ensuring cross-device accessibility and consistent tracking, as required for cross-channel campaigns.

D. Alert+inbox consume 1 supermessage (Correct)
Explanation: In MobilePush, sending an Alert (a push notification that appears on the device’s lock screen) and an Inbox message (stored in the app’s message center) together counts as one supermessage. A supermessage is a billing unit in Marketing Cloud that represents a single message delivery, regardless of whether it includes both an Alert and an Inbox component. For example, sending a promotional message that appears as a push notification and is saved in the app’s inbox consumes one supermessage. This ensures cost efficiency while delivering messages across both delivery methods.

Why it’s correct: Salesforce documentation specifies that combining an Alert and Inbox message in a single send counts as one supermessage, optimizing resource usage.

References:
Salesforce Help: App Inbox Messaging – Confirms support for public URLs and contact-centric message ownership.
MobilePush App Configuration - Trailhead – Explains Inbox message configuration and supermessage billing.
Salesforce Marketing Cloud Advanced Cross Channel Exam Guide: Covers MobilePush features, including Inbox messages, URL flexibility, and supermessage counting.