Delivery tracking: Delivery and operations
Suppresses recipients after a hard bounce or spam complaint, distinguishes transient failures, honors List-Unsubscribe, and never retries delivery to a suppressed address.
Event streams roll into digest batches keyed by recipient and channel, with deduplication, cutoff schedules, partial-failure isolation, and idempotent send tokens so duplicate workers cannot deliver the same digest twice or drop unreadable aggregates silently.