How to set custom MIME type for application?

Question

In my app i want to interact with Gmail app. I need to open attached files with custom extension. I try this solution:

<data android:mimeType="application/*"
      android:pathPattern=".*\\.mms"
      android:scheme="file" />
<data
      android:mimeType="application/*"
      android:pathPattern=".*\\.mms"
      android:scheme="content" />

but it bind my app for all extension. I try to add existing MIME type rule:

<data android:mimeType="text/plain"/>

and it is works fine for me. So, how i can add custom MIME type?