Green’s Dictionary of Slang

1. to send someone to buy liquor illicitly.

a.1977

Casey ‘Kid’ Motsisi in Casey & Co. (1978) 64: Once in a while you found a gweva who was as dirty as his face and his rags. You mail him for a bottle of mahog. What does he do? He creeps back with a bottle of cheap vino. Gives it you on the sly at a street corner and scuttles.

2. to act as a go-between in such a purchase.

1980

E. Joubert Poppie 209: I know this man, I see him walking up and down, he’s a mailer. For whom does he mail? He carries drink to the shebeen queens.