"How Did That Chain Letter Get To My Inbox?" More on recent chain-letter transmission research:

...Rather than spreading like a virus, with each message producing many direct "descendents" in the tree diagram, the data suggest that people are selective in forwarding messages to others in their social networks. For example, the researchers discovered that 90 percent of the time, the messages produced only a single descendent.

These messages also rarely took the most direct route between two inboxes, even when two people were connected by a few degrees of separation. "The chain letters themselves often got to people by highly circuitous routes," [Cornell researcher Jon] Kleinberg explains. "You could be six steps away from someone, and yet the chain letter could pass through up to 100 intermediaries before showing up in your inbox."