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.