Hi
I am getting this message on my Exchange server about every 20 minutes:
The average of the most recent [516] heartbeat intervals 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.

Some research indicates:
“…firewall has not been configured to let HTTP(S) requests live longer than the minimum heartbeat interval“. The default setting is 9 minutes (540 seconds).

My Firewall is a Vigor V3300 - port 443 is open for TCP/UDP but I cannot find where I can configure this timeout.
Any help appreciated. Thanks.