The Service Monitor reports which of the following?

The Service Monitor in Mimecast provides insights into the various delivery routes that emails take through the Mimecast system. This includes monitoring the performance and health of the pathways that emails follow, ensuring that they are processed efficiently and that any potential issues can be identified and resolved quickly. By focusing on delivery routes, users can gain valuable information about how emails are routed, any delays that may occur, and overall service reliability.

Monitoring delivery routes is critical for maintaining optimal email flow and troubleshooting potential disruptions, making this the correct choice in the context of what the Service Monitor reports.