Written and first recorded by Shuggie Otis (1971).
Hit version by The Brothers Johnson (US #5/Soul #1 1977).
From the wiki: “Shuggie Otis wrote the song for a girlfriend who used strawberry-scented paper when she wrote letters to him. He recorded it for his 1971 album Freedom Flight. George Johnson of the Brothers Johnson was dating one of Otis’ cousins when he came across the album Freedom Flight. The group recorded ‘Strawberry Letter 23’ for their 1977 album Right on Time, which was produced by Quincy Jones.