[1] : Jargon File (4.3.1, 29 Jun 2001)

snail-mail n. paper mail, as opposed to electronic. sometimes written
   as the single word `snailmail'. one's postal address is,
   correspondingly, a `snail address'. derives from earlier coinage
   `usnail' from `u.s. mail', for which there have even been parody
   posters and stamps made. also less commonly called `p-mail', from
   `paper mail' or `physical mail'. oppose email.


see also:
email 

Snail-Mail >> S Words
Snail-Mail, definition of term: Snail-Mail
snail-mail_pag1.html