Via Flutterby [1] this wonderful page about tunnelling TCP/IP over SMTP. [2]
Yes, you read right—a way to tunnel TCP/IP over the SMTP protocol, which itself runs over TCP/IP. The author of the page states that this is for firewalls so restrictive that only email passes through. Issues of latency aside, is seems so … convoluted … to do such a thing.
But remember—the Internet sees censorship as damage and routes around it. Often times in ways people don't expect.