Because iCloud Drive is now properly integrated into iOS 9, you can insert items from it into your
Mail messages. Just tap and hold the message area while composing, and then select Add Attachment from the menu that pops-up (if you don’t see the option, tap the right-facing arrow on the menu).
However, as the TV adverts say – that’s not all! By tapping the Locations link at the top left of the iCloud Drive file listing, and then the More link, you can opt to connect to any other cloud storage service that you might have installed (and that has a sharing extension), such as Dropbox, Google Drive, and Microsoft OneDrive.
Some apps like the Quip collaborative word processor will also let you add files from their cloud-based file store using this technique. Notably, if an incoming message contains an attachment then you can also save it to your cloud services too – just tap and hold, then select the Save Attachment icon, and select your cloud service of choice in the way described previously.