Use the sources for different questions
Provider delivery events and DMARC aggregate reports can illuminate the same sending stream without identifying the same individual messages. Provider events describe handling observed by the sending service, often with provider-specific message or event identifiers. DMARC aggregate reports summarize authentication-related observations made by reporting receivers over a period. A useful investigation combines their perspectives while preserving differences in scope, timing and identifiers.
RFC 9990 defines DMARC aggregate reporting. Twilio SendGrid's event reference provides one concrete provider event vocabulary. Neither source establishes that EmailAuth can automatically join their records at message level. This article proposes a timeline method and does not retrieve actual provider events, reports or recipient data.
Interpret delivery events at the documented boundary
In the SendGrid reference, processed means the provider accepted and can deliver a message. Delivered means it succeeded in delivering it to the receiving server. Deferred means the receiving server temporarily rejected it, while dropped identifies provider-side reasons for not proceeding. Preserve the original event and diagnostic details under the provider's definitions. Do not substitute a universal interpretation for similarly named events from another service.
Delivery to a receiving server is not the same as inbox placement or a person reading the message. A later engagement event, where available, has its own measurement limitations and should not be used to rewrite delivery semantics. Keep submission, transfer, filtering and engagement as distinct stages. A business stakeholder may ask whether a customer saw a notification, but the available provider event may answer only whether the receiving server accepted it.
Understand what aggregate reports summarize
DMARC aggregate reporting concerns domain-authentication observations and associated policy information, not a complete recipient-level delivery ledger. RFC 9989 defines the authentication and alignment framework that those observations describe. A reporting row can summarize multiple messages with shared characteristics. It should not be expanded into invented individual messages merely to match a provider event table.
Report coverage depends on the reporting receivers and retained periods. Absence of a report does not prove that no mail was sent, and a reported authentication result does not establish inbox placement. Record the report source, period, count dimensions and interpretation limits. Avoid assuming that every receiver sends reports or that every sending stream is fully represented in the available collection. The analysis should show where the sources overlap and where they remain incomparable.
Separate event time, collection time and report period
A provider event timestamp, a webhook arrival time and a report's covered interval are different clocks. An ingestion delay can make a recent dashboard update describe older message handling. A daily aggregate can include observations across an interval rather than one exact send time. Normalize time zones for comparison while preserving the original values and their meaning. Do not silently substitute the ingestion timestamp for the event timestamp.
SendGrid's webhook documentation describes retries for non-2xx responses over a rolling period of up to 24 hours per event. That can affect when telemetry arrives without changing when the underlying mail event occurred. The documented behavior is specific to that service. Other providers need their own retry and timestamp evidence before their events are placed on the same analytical timeline.
Join only where identifiers support the claim
For provider events, use the documented identifiers and recipient scope needed to distinguish events about the same message. Protect recipient information and do not assume a provider message identifier is globally unique across accounts or environments without checking its documented scope. For DMARC aggregates, use the available domain, source and period dimensions as supported by the report. The intersection may justify a stream-level comparison rather than an exact message join.
Label the linkage strength explicitly. A deterministic identifier match within a documented scope is different from temporal proximity, a shared IP address or a common domain. A shared infrastructure address can represent multiple streams. An apparent count match is not proof of one-to-one correspondence. Where the records do not permit exact linkage, state that the timeline concerns the stream and avoid language such as “this report proves what happened to this individual message.”
A two-track timeline worksheet
Create a provider track with account or stream reference, event type, provider identifiers, event time, collection time, diagnostic and scope. Create a report track with reporter, report identifier, covered interval, source dimensions, counts and authentication observations. Add a linkage column describing the shared dimensions, known exclusions and confidence limits. Keep the original source records in approved storage and use redacted references in the working summary.
The analysis section should state the question, such as whether a policy change coincided with more authentication failures in a particular stream. Record alternative explanations, including traffic mix, missing sources, provider retries and configuration changes. A temporal association can justify investigation without proving causation. Do not attribute every deferral to DMARC merely because a policy changed during the same week; the actual receiver diagnostic and authentication evidence matter.
Fictional diagnosis: deferred events and a passing aggregate
A fictional billing stream shows provider deferrals during an afternoon, while a receiver's aggregate for the day contains many aligned passes. The team initially treats the passing aggregate as a contradiction that disproves the deferrals. The proposed review instead asks whether the same stream, receiver, period and message population are represented, and what reason the provider diagnostics give for temporary rejection.
The evidence could be compatible: domain authentication may pass while a receiver temporarily rejects some traffic for another reason, or the aggregate may cover a different subset. Those are hypotheses, not fabricated findings. No event, report or receiver was queried for this example. The team would retain the uncertainty and seek authorized source evidence rather than manufacturing message-level links to force a single narrative.
Present conclusions at the right granularity
A defensible summary might say that provider telemetry shows temporary rejection for a defined stream while available aggregate reports show a particular authentication pattern over a broader interval. It should state the missing overlap and avoid concluding that every reported pass reached an inbox. The summary can still identify a useful next investigation without pretending to have complete visibility.
The catalogue requires one message or stream timeline without implying exact message linkage where identifiers do not permit it. That original timeline remains open. This draft supplies the method and fictional scenario, not real linked evidence. Human specialist review, source applicability, production routes, accessibility and owner release also remain open. Publication requires authorized retained records, a reproducible linkage method and explicit coverage limitations, with no unnecessary recipient data exposed.