As per @pedronis comments above, it seems fair to assume users would save / add attachments from removable media, and given that this is done with user-interaction, the same use-case as for web browsers applies in respect to removable-media auto-connect - this has now been updated in the Process for aliases, auto-connections and tracks. Also given that this is published by the official upstream, granting auto-connect of removable-media for hey-mail. This is now live.