Satya's blog - Masers

The good folks of ASR, Steve VanDevender in particular, have just stumbled upon the MASER: Mail Amplification by Stimulation of Emitted Rejections.

This is described as a mail loop created by... well, anything really, but typically due to automatic forwards that point to each other. An example would be sending a vacation auto-message to a mailing list, which sends it to the sender (and everyone else), which auto-responds again, etc. The "Amplification" happens when the vacation program quotes the original message.