How to detect “silent filtering” where messages are delivered but unseen?

Detecting silent spam filtering:

Symptoms:

High delivery rate, very low opens

Provider-specific engagement drop

No bounces but no activity

Detection methods:

Seed testing: Send to test accounts at various providers. Check spam folder placement.

Engagement comparison: Compare open rates by provider. Dramatic differences indicate filtering.

Direct verification: Have real users check their spam folders.

Panel data: Third-party services tracking actual inbox placement.

Time pattern: Zero opens immediately versus zero opens after initial opens may indicate different issues.

Silent filtering is harder to detect than bounces. Requires proactive monitoring.

Cargo delivered to the warehouse but locked away where no one can find it.