The arrest happened Wednesday in Brookings, S.D., just hours after the Postal Service announced it was discontinuing Saturday service.
An officer tracked down the mail carrier, who was reported for allegedly boozing on the job, according to the Brookings Register.
The officer noticed an open container of alcohol in the main truck so he gave the 33-year-old suspect a field sobriety test, The Yankton Press & Dakotan reported.
The suspect's name has not been released, but his blood alcohol level was found to be above the .08 legal limit, Lt. Derrick Powers told reporters.
The carrier was taken to the Brookings County Detention Center, according to the Associated Press. No other information was given.