This is not a altogether new bug. I've had previous encounters with missing attachments from recipients of outlook emails. I'm paraphrasing memory but I when I last hit this a few years ago I found two KB articles pertaining to dropped attachments- one said to not use Word as the email editor, the other said don't send in plain text. (scout's honor) And from the Exchange 2007 deployment doc: "The Exchange 2007 MIME parsing engine, developed and evolved through many years of MIME handling exposure, is likely the most trusted and robust MIME engine in the industry".