Originally recorded by Wayne Carson Thompson (1969).
Hit version by The Box Tops (US #18/UK #22/CAN #9/AUS #7 1969).
Also recorded by Gin Blossoms (1994).
From the wiki: “Wayne Carson Thompson performed professionally as ‘Wayne Carson’, and was a Nashville-based musician, producer and songwriter. Among his songwriting credits were ‘The Letter’ (also recorded by The Box Tops), ‘Always On My Mind‘, and ‘She’s Actin’ Single (I’m Drinkin’ Double)’.”