What metrics actually indicate inbox success?

Meaningful inbox success metrics:

Open rate by provider: Compare opens across Gmail, Outlook, Yahoo. Drops at specific providers indicate placement issues.

Engagement rates: Clicks, replies, forwards. Deeper engagement signals inbox visibility.

Complaint rate: Low complaints indicate recipients find value. High complaints signal problems.

Postmaster scores: Reputation ratings from Gmail and Microsoft reflect provider trust.

Seed test results: Direct placement observation across providers.

Delivery rate alone is not an inbox metric. You can have 99% delivery and 50% spam placement.

Measure what matters: are recipients actually seeing and engaging with your mail?