snail mailn. Informal Mail delivered by a postal system, as distinct from electronic mail.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.snail mail n (Communications & Information) the conventional postal system, as opposed to electronic mail vb (Communications & Information) (tr) to send by the conventional postal system, rather than by electronic mail [C20: so named because of the relative slowness of the conventional postal system]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014snail? mail` n. physical delivery of mail, as contrasted with electronic mail. Also called s-mail. [1980?85] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.