How to diagnose multi-brand shared domain problems?

Multi-brand shared domain diagnosis:

Identify contamination source:

Which brand's sending correlates with issues?

Review metrics per brand/stream

Check complaint sources

Common problems:

One brand's poor practices affecting all

Combined volume exceeding safe levels

Mixed reputation signals confusing providers

Solutions:

Isolation: Move brands to separate subdomains

Policies: Enforce strict standards for all brands

Accountability: Track metrics per brand

Prevention:

Separate domains/subdomains from start

Shared domain policies enforced

Regular auditing per brand

Ships from same fleet share reputation. One problem vessel affects all.