The Avaya IP Office Server Edition is designed for scalability, supporting a large number of users across multiple servers. The maximum capacity is 2500 users (Option D), achieved in a fully expanded deployment with a Primary Server, Secondary Server, and multiple Expansion Systems (up to 148 additional systems).
This capacity includes all types of users (e.g., Basic, Power, Teleworker) and requires sufficient licensing and hardware resources (e.g., virtualized or dedicated servers). Options A (500), B (1000), and C (2000) represent lower tiers or partial configurations but do not reflect the full potential of Server Edition.References: Avaya IP Office Server Edition Capacity Guidelines.

The IP Office Server Edition Expansion System extends capacity and is managed by the Primary Server.
Option C, "It supports up to 250 users," is true, as each Expansion System (e.g., IP500 V2 or Linux-based) supports up to 250 users, contributing to the total 2500-user capacity. Option A is false as Voicemail Pro can be centralized on the Primary Server. Option B is incorrect because Expansion Systems rely on the Primary Server for operation. Option D is false as they support analog, digital, and IP endpoints.References: Avaya IP Office Server Edition Deployment Guide.