Great tip from Micah Gilman's Blog.
By default, Appel's Map app displayed images, PDFs and other Mac-viewable content as an inline image. This gets really annoying for many (including me). Fortunately Micah figured out a tip to make attachments appear as icons by default. To make this the default behavior, open Applications --> Utilities --> Terminal and type:
defaults write com.apple.mail DisableInlineAttachmentViewing -bool yes
If you decide this isn’t what you’re looking for, to restore inline attachment viewing type:
defaults write com.apple.mail DisableInlineAttachmentViewing -bool false
Restart Mail and you’re back to normal.