USPS delivery, deprecatingly (5,4)

I believe the answer is:

snail mail

(Other definitions for snail mail that I've seen before include "traditional post" , "The conventional postal service" , "Modern jargon for letter post, mollusc-slow compared to electronic transport" , "Postal system (facetious)" , "old-fashioned correspondence?" .)

I've seen this clue in the Universal.

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