A single send generates a sequence of delivery events over its lifecycle: accepted by the sending platform, accepted by the receiving server, and then whatever engagement or failure events follow, such as a bounce, a spam complaint, an open, or a click.
Open and click tracking are probabilistic and increasingly unreliable as a completeness signal (image-blocking, privacy-preserving mail clients, and proxy-based prefetching all distort them), while acceptance, delivery, bounce, and complaint events are comparatively reliable, protocol-level signals.
Delivery events are the raw material behind both webhook notifications and any dashboard-level delivery reporting; the event log itself is the source of truth, not a derived summary.