I am getting this warning message on an Exchange 2010 server running on Windows 2008 R2
All roles are installed on this one server, we have increased the firewall HTTPS timeout to 1 hour and the server IIS time out to 30mins but to no effect. Firewall used is Juniper.
IIS setting changed is in the Default website - ASP - Session Properties - Timeout
Log Name: Application
Source: MSExchange ActiveSync
Date: 26/09/2013 9:57:58 PM
Event ID: 1040
Task Category: Requests
The average of the most recent heartbeat intervals  for request [Sync] 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.
For more information about how to configure firewall settings when using Exchange ActiveSync, see Microsoft Knowledge Base article 905013, "Enterprise Firewall Configuration for Exchange ActiveSync Direct Push Technology" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=905013
<Provider Name="MSExchange ActiveSync" />