how can i block email attatchments from downloading?
About the only setting you can change that pertains to this is the Load Remote Images toggle that is found in the Settings app under Mail, Contacts, Calendars. Most important thing, still, is to make sure that is off.

This may or may not do the trick for you. I get the feeling this switch was designed more for the retail emails that are sent out - full HTML with tons of images.

Have you performed your test with a PDF file? By default iOS creates an icon for you to tap before it downloads the attachment. It is possible this switch is on, and it is downloading images.

If the afore-mentioned ideas don't work, would it be possible to not open emails that have the paperclip icon next to the Subject/Sender, and instead wait until you were on a wifi? This could protect from data usage, however, if you must receive large quantities of large attachments for a specific purpose this may not be practical.