Android :: Creating A Default Viewer - Receiver For Email Attachments

I'm trying to create a default handler for .p7s/.p7b files in Android.

I figured the best start would be to create a BroadcastReceiver that will capture the intent from the Android email application (or K-9 if that's a need) for opening of certain attachments (filtered by mime type). Specifically I'm trying to handle s/mime email so looking for the "application/x-pkcs7-certificates" and "application/x-pkcs7-certificates" mime types.

Just as a basic test I've been trying something like this:

CODE:..........

I've tried using the following mimeType filters as well (testing signatures first):

CODE:................

I can't seem to get the IntentReceiver class to capture the intent no matter what filtering I use though. Am I going about this the wrong way?