Given the Marketing Cloud Connect integration is already in place and the requirement is prompt, near-immediate delivery when a new subscriber signs up on the website (implying the website submission creates or updates a corresponding Salesforce record, since Sales Cloud is the connected CRM), Salesforce Triggered Sends is the correct, native mechanism: configured declaratively against the relevant Salesforce object and field (such as a new Contact/Lead record being created), it fires the welcome email promptly upon that Salesforce-side event, leveraging the existing Connect integration rather than requiring a separate capture mechanism. Batch file drops to SFTP (A) and file imports to data extensions (B) are both inherently scheduled, delayed, batch-oriented processes that cannot deliver the ' promptly ' requirement, since they depend on periodic file processing rather than immediate, event-driven triggering. Smart Capture forms (C) are a native Marketing Cloud web-form capture tool, but the scenario specifically anchors the integration around Sales Cloud via Marketing Cloud Connect, making a Salesforce-side triggered mechanism the more directly applicable and efficient solution that leverages the existing architecture rather than introducing a parallel Marketing Cloud-native capture form. Reference: Salesforce Triggered Sends, Marketing Cloud Connect.