The requirement is to send emails from the owner of the customer's account. Marketing Cloud Account Engagement provides a specific sender option called "Account Owner." When this setting is selected for an email send, the system dynamically populates the sender's name and email address with the information from the user who owns the Salesforce Account record associated with the recipient prospect. This directly and efficiently fulfills the stated business requirement without needing custom configurations. This feature is designed to personalize communication and align it with account management structures in the CRM.

A. Set the sender of the email as a specific user. This option is static and would send all emails from a single, predefined user, failing to meet the dynamic requirement based on account ownership.

B. Set the sender of the email as a custom CRM user. This is not a standard, out-of-the-box sender setting. While achievable with workarounds, it is not the direct or intended solution for this common use case.

D. Set the sender of the email as the assigned owner. This option uses the owner of the prospect record (Lead or Contact owner), which can be different from the Account Owner, thus not meeting the specific requirement.

1. Salesforce Help, Marketing Cloud Account Engagement Documentation, "Considerations for Sending Emails." This document outlines the available sender options for emails. Under the "Sender" section, it explicitly lists "Account Owner" as an option, described as: "The user assigned as the account owner for a prospect who is associated with an account." This directly supports the correct answer.

2. Salesforce Help, Marketing Cloud Account Engagement Documentation, "Sending Emails with a Variable Sender." This guide details the process for setting up dynamic senders. It specifies the different variable sender types, clearly distinguishing between "Assigned User" and "Account Owner," reinforcing that "Account Owner" is the correct choice for this scenario.

3. Salesforce Help, Marketing Cloud Account Engagement Documentation, "Variable Tags in Account Engagement." This resource explains the different user-related variable tags. It shows distinct tags for the assigned user (%%assigneduser...%%) and the account owner (%%accountowner...%%), which technically underpins the functional difference between the "Assigned User" and "Account Owner" sender options.