I am getting this error on Exchange2016 event veiwer:
The average of the most recent heartbeat intervals  for request [Ping] used by clients is less than or equal to .
Make sure that your firewall configuration is set to work correctly with Exchange ActiveSync and direct push technology. Specifically, make sure that your firewall is configured so that requests to Exchange ActiveSync do not expire before they have the opportunity to be processed.
How to check and fix it?