Apple Mail is a pretty decent email client, but it saves all your attachments in a folder deep within your user library, sucking up disk space without ever really letting you know. Fortunately, this is an easy problem to solve if you know where to look. Sort of, anyway. Apple made removing your attachments very simple, but if you want to actually save and archive them it can be a bit more complicated—especially if you're running Lion. But not to worry, we'll walk you through the whole thing. The process can be a little tedious, but it's not too tough.
Some tips from Gizmodo about cleaning up attachments from Apple’s Mac OS X Mail application.