What are the main indicators of reputation collapse?

Signs of reputation collapse:

Open rate crash: 50%+ drop across campaigns, especially at specific providers.

Complaint rate spike: Rising above 0.3% at any provider.

Gmail Postmaster: Domain reputation drops to "Low" or "Bad".

Bounce pattern change: New types of policy blocks appearing.

Blocklist presence: Listings on Spamhaus or other major lists.

Engagement collapse: Clicks and replies disappear.

Seed test results: Spam folder placement increases dramatically.

Throttling: Deferrals and rate limiting increase.

Multiple indicators together confirm collapse rather than normal variation.

When multiple warning lights come on simultaneously, the ship is in real trouble.