Plan the architecture
before you send.

Reputation accrues per domain. Several brands sharing one sending domain share one reputation and one DMARC policy, so the least careful brand sets the ceiling for the most careful one. Separating marketing from transactional does the same job in miniature.

This produces a subdomain per brand per stream, plus tracking and return-path names, plus an organisational DMARC record — and the reasoning for each. It is a starting architecture, not a mandate; the important part is that the decision is deliberate rather than inherited.

Every new subdomain starts with no reputation, and no reputation is treated as suspicious. Pair this with the warmup planner rather than switching full volume onto a fresh name.