Outlook is quite open for integrations and well documented. You need to choose what tool you want to use. Easy enough to use VBA in outlook and create a rule that runs your code when a new email arrives. Then if it meets your criteria you can create a text file, print, forward whatever.
I'm not sure about integration with PHP but I get the feeling this is not a php question. Try the forums at www.universalthread.com - they will be more appropriate.