Domains used for bulk outbound email are typically separated from the normal corporate email domain to prevent employee emails getting blocked at customer mail

Domains used for bulk outbound email are typically separated from the normal corporate email domain to prevent employee emails getting blocked at customer mail gateways by anti-spam heuristics. Practically every large org gets burnt by this once, learns their lesson, and then splits their domains. Microsoft has something like a hundred domains, including purposefully misspelled ones like "microsft.com", which is real, owned by them, and regularly used to bypass "security filtering" by paranoid admins.