Newer Movie, Older Premise

Tonight we watched "You've Got Mail". It is a modern version of the story we saw yesterday, "In The Good Old Summer Time". Tom Hanks and Meg Ryan star in the modern version. It is cute. Both still hold up today. The older version starred Judy Garland and Van Johnson. The setting of the story wasn't modern, but it was believable. I enjoyed both of the movies. Now I'm wondering who the original writer of the story/premise was? I wonder if the newer movie states who the writer had been? If not, I wonder if it's plagerism?