What kind of file extension are you trying to download, and what - specifically - is happening when you try to download attached files from your emails? Also - are you accessing email via the PlayBook mail app or something else?
I've never had any particular trouble downloading attachments, but I do know that if it's a file type that is not one of the standard types for the file manager, finding them isn't obvious. For example, if I download an epub file from an attachment, it doesn't show up in the file manager, but I can still navigate to it via my ebook app.
