Spamassassin almost cost me my career. A manager at a big company over a team doing my "dream job" emailed me, and Spamassassin threw it straight in to the bit bucket for whatever arbitrary reason it did. Fortunately a recruiter at said company was more persistent and managed to get through to me by phone. That job ended up catapulting me onto a career "hockey stick," and if it weren't for that, I'd likely still be languishing in some sad corner of IBM.