How is a service delivered between departments of the same organization classified?

While 'internal' describes the delivery scope, it is not the formal ITIL classification used to categorize services based on their importance and criticality to organizational operations.

External service refers specifically to services delivered to customers or stakeholders outside the organization, which is the opposite of an inter-departmental delivery scenario.

In ITIL service management, a service delivered between departments of the same organization is classified as a mission critical service because it underpins essential internal operations that the organization depends on to function. Disruption of such inter-departmental services directly impacts core business activities, making mission critical the appropriate classification for services that are vital to organizational continuity.

Organizational service is not a recognized or defined service classification within the ITIL service management framework.