Android : Extend Droid's Default Gmail / Email Applications?

I would like to extend the Android platform's default Gmail/Email applications either by plugging into their ContentProvider or by using intent filters. Essentially, I want to be able to scan incoming emails for special rules that will trigger events in my Android application. If scanning emails automatically isn't possible, then I would at least like to add a menu item to the email viewer screen that would allow the user to flag the email content as needing to be scanned.

Does the Gmail/Email applications allow you to extend them in this way?

For future reference, besides finding sample code or reading documentation provided by the author of an application, is there a standard way of finding out what intents are available for my application to use? Like a tool maybe?