Written and first recorded by Shuggie Otis (1971).
Hit version by The Brothers Johnson (US #5/R&B #1/CAN #8/UK #35 1977).
From the wiki: “Shuggie Otis, son of famed songwriter (‘Willie and the Hand Jive’), bandleader and disc jockey Johnny Otis, wrote the song for a girlfriend who used strawberry-scented paper when she wrote letters to him. Otis recorded it for his 1971 album Freedom Flight. George Johnson of the Brothers Johnson was dating one of Otis’ cousins at the time when he came across an early pressing of the album. The Johnsons recorded ‘Strawberry Letter 23’ for their 1977 album Right on Time, which was produced by Quincy Jones.