The build order matters: domain and inbox architecture first, list and data second, sequences last. Sending at volume from your primary domain is how deliverability dies, so outbound gets its own protected domain and warmed inboxes before the first email leaves.
For a B2B SaaS company moving off paid social we set up seven inboxes on a dedicated domain as part of the engine. For a newly funded FinTech, the same system re-engaged 131 dormant leads with tailored sequences instead of letting the database go cold.