Not quite Snail "mail"... however, Ami Ben-Bassat has a nice post on an experiment with snail data transfer.
System architecture: the system is constructed of a back end - a carriage, Ben-Hur movie style, which is made of a yoke made of light Balsa, and outfitted with two huge wheels - 2 DVD wheels, 4.7 Giga each. The front end, to which the carriage is harnessed consist of a Giant snail (Achatina fulica), known also as Giant African Snail (Africans are known as the world fastest runners ).Conclusion.... data transfer via snail is faster than ADSL :)