I am very pleased to let you all know that in response to your feedback we are adding support for User Datagram Protocol (UDP) notification functionality back into Microsoft Exchange Server 2010. ...
Updated Jul 01, 2019
Version 2.0
Blog Post
have you done the following:
Subkey location: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesMSExchangeRPCParametersSystem
Subkey name: EnablePushNotifications
Type: REG_DWORD
Value: 1
Subkey location: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesMSExchangeRPCParametersSystem
Subkey name: EnablePushNotifications
Type: REG_DWORD
Value: 1