Re: Emails with attachments not downloading in native Touchwiz Em
If you long press the little arrowhead to the right of the attachment, it will drop down revealing the name of the attachment along with a floppy disk icon to the right. If you touch that, it will save the attachment to your downloads folder. I don't believe there is a setting to automatically download all attachments.
I would suggest either using the Gmail app (though you have to install another app in order to attach docs to an email) or, what I use, K-9 Mail from the market. K-9 is great, but it's a little bit of a pain to set it up. However, once it's set up, you're done and it works great!
Hope this helps...