✅ Comprehensive and Detailed Explanation:

This is a classic transactional use case involving multiple channels: if the password reset email fails to send, the system must fallback to SMS delivery.

The best-practice solution is to:

Use a Transactional Send API for password reset emails.

Use the Event Notification Service (ENS) to monitor delivery or bounce events in near real-time.

Based on failure status, trigger an API call to initiate an SMS message.

D is the only option that uses Salesforce’s native ENS and API infrastructure for near real-time failure handling, which meets the requirement for “timely delivery.”

❌ Why Other Options Are Incorrect:

A. The Not Sent data extract is not real-time and is typically processed in batch — not suited for password resets that require instant fallback.

B. Engagement Splits (e.g., link clicked) are not ideal for determining whether an email was delivered or not. Plus, password resets don’t rely on email clicks — they’re more about deliverability.

C. API responses for triggered email sends do not reflect actual delivery success or failure — they only reflect submission status. You need ENS to monitor actual send results.

Exact Extracts from Salesforce Documentation:

Salesforce Event Notification Service (ENS): "ENS sends near-real-time email delivery, bounce, or click events to external systems so you can monitor transactional sends and take automated actions (e.g., triggering an SMS)."

— Source: https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/ens-overview.html

Transactional Email via API: "Use the Transactional Messaging API to send password resets or other 1-to-1 emails. Integrate with Event Notification Service to determine the outcome of each message."

— Source: https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/sendTransactionalEmail.html

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