Different clocks, different events
The message Date field, a server's receipt time, a mailbox delivery property and a file's filesystem timestamp should not be treated as one interchangeable creation time. A displayed value may also have been converted by the viewing application. The RFC message date represents the originator's asserted origination time, not an independent certificate of delivery.
Make the conversion visible
For a fictional example, 09:00 with an offset of +08:00 and 01:00 UTC identify the same instant. Preserve the original value and offset before normalising a chronology. Record the timezone used in reports and account for daylight-saving rules where relevant. Avoid silently interpreting a timezone-free value as the examiner's local time.
Resolve before accusing
A one-hour or eight-hour discrepancy can arise from interpretation or presentation. It can also coexist with a genuine inconsistency. Compare timestamps from independent sources, examine clock reliability where evidence permits, and state uncertainty rather than forcing an exact sequence. An export or migration can add new file dates without changing the date asserted inside the email. A timeline should distinguish observed values, calculated conversions and inferred events.
Sources & further reading
Primary references support the technical explanation. They do not establish D3 validation of a particular method.