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Exchange ActiveSync Heartbeat

Autor brendon

Most people don’t realise this but for ‘Push’ email to function, the “Client” must keep an open TCP session to the “Server”. Outlook (by default) does this using RPC over the LAN or VPN, constantly exchanging data, even when there is no new information to send.

Mobile phones are a little different, for one they use HTTPS to sync data. Secondly, data traffic is generally more expensive so when there is no new data, you want the phone to send as few data packets possible. When you create a ‘Publish Outlook Anywhere’ rule with ISA 2006, this automatically configures the firewall to let TCP sessions stay open for up to 30 min without seeing any traffic. Meaning that when there is no new email, the phone will send a single data packet every 30 min.

Unfortunately if your running any other type of firewall (ASA, PIX, NetGear, ISA 2004, etc.) you will need to manually configure this setting. By default, most firewalls will forcefully close a session that is idle for 5 min for security reasons AND on most SOHO firewall’s you can’t change this setting.

Moral of this story, if you use ActiveSync with push enabled on client mobile phones and don’t use ISA 2006 as your Internet firewall, you will likely have sessions from mobile devices disconnected causing Error 3033 on the Exchange Server Event Log. There is a Microsoft KB Article that shows simple change you can make to the ActiveSync web.config file to specify the maximum TCP session limit for your firewall to 5 min. eg,

<add key="MinHeartbeatInterval" value="60"></add>
<add key="MaxHeartbeatInterval" value="300"></add>