Which of the following represents an unsupported directory system for Mimecast?

The correct answer represents a directory system that Mimecast does not support. Exchange 2010 is outdated compared to later versions of Exchange, such as Exchange 2013 or Office 365. Mimecast has adapted its services to align more closely with current technologies, and as a result, it may lack compatibility or provide limited functionality for older systems like Exchange 2010.

In contrast, platforms like Office 365, Exchange 2013, and Google Workspace are widely supported as they represent more modern and commonly used directory systems. Since Mimecast continually updates its integration capabilities to accommodate advancements in technology, it supports those newer systems while older ones, such as Exchange 2010, fall out of the support range. Therefore, Exchange 2010 is classified as an unsupported directory system in the context of Mimecast services.