How to verify connectivity between MDM server and Apple Push Notification Service (APNs)?

Description

APNs (or Apple Push Notification Service) is free notification service provided by Apple and used by ManageEngine Mobile Device Manager Plus for managing iOS devices. To use APNs, you need to create an APNs certificate and upload it on MDM server. Once done, you can verify if the server can contact the APNs as explained below:

Steps

• Firstly, verify if telnet has been installed or not. On the machine running the MDM server, open Command Prompt as an Administrator.
• Now, type in the command telnet. If command is not executed, you need to install/enable telnet.
• To enable telnet type in the command pkgmgr /iu:"TelnetClient". If you're unable to execute the command, you can use the command dism /online /Enable-Feature /FeatureName:TelnetClient. 
• Now, restart the machine and open Command Promt as an Administrator.
• Execute the command telnet api.push.apple.com 443.
• If you can establish a connection successfully, it implies the MDM server can contact Apple Push Notification Service (APNs)