A customer wants to configure appointment reminders for patients in their clinic.

A Salesforce Data Entry Source configured against the appointment date field (a date-based/date-triggered entry source) natively evaluates each record ' s scheduled date and injects the patient into the journey exactly one day before the appointment at the specified time, eliminating the need for a separate daily refresh automation. Once in the journey, an Email activity sends the reminder, and an Update Contact/Salesforce Write-Back activity updates the appointment record directly back in the CRM (Sales/Service Cloud) to reflect the reminder was sent — closing the loop where the source of truth actually lives. Option A is close but writes back to ' CRM ' generically through a Data Extension entry source, missing the more precise Salesforce Data Entry Source that natively supports date-based triggering off the CRM record itself. Option B relies on manually engineered AMPscript logic to update a Synchronized Data Extension, which is a read-optimized, one-way sync object not intended for write-back to Salesforce — updates must go through the CRM directly. Option C similarly targets the read-only Synchronized Data Extension for the write-back rather than the actual CRM record. The correct pattern uses Salesforce Data-based entry timing and a genuine CRM write-back activity. Reference: Journey Builder Salesforce Data Entry Source, Update Salesforce Data/Write-Back.