Granny Smith

George Harrison wrote and recorded with The Beatles a song called Love You To.  The working title for the song was Granny Smith.  The song was recorded beginning April 11, 1966 and The Beatles continued recording takes of the song on the same day that Paperback Writer was recorded:  April 13, 1966.
I ran down the possibilities for the title:  genealogy of George's or his wife, Pattie and the Magritte painting that the Paul replacement owned (the big green apple painting called "Le Jeu de mourre" ["The Guessing Game"]).  I couldn't trace a Smith to George or Pattie Boyd and the painting dates from the summer of 1967.  The married name of John's Aunt Mimi was Smith, but there is nothing to suggest that George called her Granny.

But Granny Smith is the name given to isolated old women by UK postmen for whom the Royal Mail service is a lifeline (per Dear Granny Smith:  A Letter from your Postman by Roy Mayall, by way of the website, http://www.culturewars.org.uk/.)

It is possible that there is a connection between George's song title and the line in Paperback Writer:  "His son is working for the Daily Mail . . . ."  Another possible clue for us all.