parcel post vs post office

parcel post

noun
  • A postal service involving the shipping of parcels. 

post office

noun
  • A place (building, office, shop, or counter) concerned with the business of delivering letters, post or mail and selling stamps, etc. 

  • A party game involving the exchange of kisses. 

  • An organisation that delivers letters. 

How often have the words parcel post and post office occurred in a corpus of books? (source: Google Ngram Viewer )