As in attachments that are of a type that the mail app doesn’t recognise as a picture/movie/etc. Can be any kind of file.
This is a workaround, more than anything.
The problem is that you can’t save it through the mail app.
Or, so I thought at least. It actually gets saved when you download the entire mail, just not the mail header.
Ok, so how do I find it?
Using a file manager (like es file explorer), and open the Download folder (internal sd if you’re using M7) or external sd (if you’re using M8 and uses external sd for attachment cache (that’s the trick btw).
Just do NOT remove the mail it’s attached to, since they go together.
On M8 it often ends up in the folder .mail that’s directly under Download.
That’s it really, just open your file manager and open the folder: and there it is. File name is a bit different though since date/time is added to it. But, you get to it at least.