Android :: Associate Application To Open Email Attachments

I've written an app that can handle the VIEW action for a given mime Type, say "application/foo". By adding the following to Android Manifest.xml the Browser automatically uses my app to open downloads of that type. The G Mail app also tries to use my app to Preview attachments of that type, but it's passing a URI with scheme "g mail-ls://" rather than a "file://" URI. I guess I need to use a Content Provider to get the attachment data, I haven't looked into that yet. But the real mystery is the Email app there just doesn't seem any way to make it open the attachments. Any pointers? Opening attachments is a very common requirement of course, and I would expect the Android platform to encourage developers to write apps to handle more mime types. Instead I couldn't find any answers.