Many organisations have complex networks that can sometimes conflict with communication of Apple devices to necessary services.

Jamf Environment Test or JET is a macOS utility designed to validate network connection for Apple devices to services such as Automated Enrolment, APNS, as well as options for adding in custom urls such as your MDM server.

The JET tool does not require admin privileges, and once it has completed its checks it will present a web view report that is easy to read. 

In addition to the network checks there is also a high level device status check with recommendations on better practices such as checking if encryption is enabled.