Nigerian 419 Scams and Spam Filters
I just received a fairly humorous Nigerian 419, so I decided to reply by saying that, "You must be mistaken; the Nigerian government does not owe me any money that I am aware of."
My reply was rejected by the scammer's spam filter! That is 100% gold, right there.
The scammer's server is running spfmilter, which I may just have to check out for myself. Thanks, Professor Ahmed Sodiq!