How do I identify if the issue is list hygiene, engagement, or technical?

Distinguishing issue categories:

Technical issues:

Authentication failures in headers

Affects all mail equally

Often sudden onset

DNS or configuration changes correlate

Engagement issues:

Gradual decline over time

Worse performance on older segments

Better performance on recent signups

No sudden trigger event

List hygiene issues:

Bounce rate spikes

Complaint rate increases

Correlates with new list additions or reactivation

Spam trap indicators

Diagnosis approach: Check authentication first (fast), then correlate timing with list/campaign changes, then analyze engagement patterns.

Is the ship broken, is the cargo spoiled, or have the trade routes dried up?