The Barnhart Dictionary Companion has an entry in Vol. 10.1 (1997) for _snail mail_ and _snail-mail_, and an entry for the verb use, and an entry for _snail mailing_. There is even an entry for _s mail_, too. "Among the New Words" (Vol. 68.4; 1993) covers this pretty well, too. David Barnhart barnhart at highlands.com