I see lots of post of setting this to 120 seconds but I do not find any official Microsoft Exchange 2010 document. Anyone know of one?
HKLM\Software\Policies\Microsoft\Windows NT\RPC
MinimumConnectionTimeout
I get random event 1040 from different users and firewall timeout has already been set.
The average of the most recent heartbeat intervals [60] for request [Sync] used by clients is less than or equal to [540]. 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.microsof