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

An Internal Service is defined as one delivered between departments or business units that belong to the same organization, where the IT department acts as an internal service provider. This classification distinguishes intra-organizational services from those delivered to outside customers or third parties.

External Services are those delivered to customers or organizations outside the service provider's own organization, which is the opposite of the scenario described.

Mission Critical is a classification based on the business impact and criticality of a service, not on whether the service crosses organizational boundaries.

Organizational service is not a standard ITIL service classification category and does not appear in the ITIL framework's service type definitions.