You can totally add a file to an email through the native email app. Just press and hold in the body of the email until the "Select", "Select All" and "Quote Level" dialogue box pops up and then hit the arrow on the end. It changes the dialogue to say "Insert Photo or Video" and "Add Attachment". Insert photo pulls up your photo library and Add Attachment pulls up the Files app.I just want to be able to open the mail app and attach a file to an email. Instead we have to go to the file and select email file.