With Exchange 2000/2003, you would simply query the 'Exchange_Mailbox' WMI class using a VBScript and trigger it with the External Process Monitor. As WMI is no longer supported in Exchange 2007, you would need to write a Powershell script do pretty much the same thing. The following article has a good example of a Powershell script you could use:
You would simply need to modify it a little to work with the External Process Monitor. Naturally, you will also need to install Powershell on the ipMonitor host.
Hopefully this gets you closer to what you need.
Chris Foley - SolarWinds - Support Specialist
Support:866.530.8040 |Direct:512.682.9385 |Fax:512.857.0125
network management simplified | solarwinds.com