Ok, now we are getting somewhere... (and this Outlook design problem was on Lollipop too. Its not a bug in Marshmallow)
I guess it might depend on what type of attachment you are opening and which app you open it with. I am dealing with attached photos (as are many others in this thread).
I can open an attached photo using Android's Gallery app, but unlike every other picture stored anywhere on my phone, the Gallery app only lets me view it, zoom in/out and go back to the email. I cannot rotate it, save it, share it or even delete it... basically
I can't do anything with the photo.
If, when I try to open an attached photo, I choose one of my file browsers (like the wonderful ES File Explorer others have mentioned here), it throws an error message: "Picture not found: /data/user/0/com.microsoft.office.outlook/app_1.1:rUfue5eY65df0fjGVw/IMG_2046.jpg"
This gives a clue that Outlook is storing the downloaded photo in a temporary, hidden, inaccessible area on the phone. I also can't browse to that directory outside of Outlook. It doesn't show up (but it still takes up space for every attachment I've ever
downloaded).
The only way I've found to deal with these attachments is to download the attachment within the Outlook email, then go back to my Inbox and click the files icon at the bottom. This brings up a list of every attachment I've downloaded - not every attachment,
mind you... just the ones I've actually downloaded from within an email - and I can then save the photo(s) from here to my device in accessible directories on my phone and use them normally.
So I have 2 copies of these things on my phone. One hidden and one useful. And I can't manage attachments from within an email other than view them in Outlook's walled garden. I have to download it within the email and then go out to the inbox file list
and then save it to my device to do anything with it. This is cumbersome and most unintuitive, but doable.
All I wanted to do was text/SMS/MMS the emailed photo to a friend. What a nightmare.
Hopefully this will help others that haven't randomly stumbled into this solution.
UPDATE: I also found if you choose to open the photo using "Outlook Image Viewer", there is a circle with a "v" in one of that app's menus that, when clicked, gives an option at the bottom to "Save to/device" but this isn't much better than the Outlook file
attachment section and most people avoid single-use apps like this when every other app easily deals with any file on your phone. You still end up with 2 copies of every file on your phone. Why doesn't Outlook just store attachments in a normal accessible
place like everyone else and avoid these headaches?