In a bid to save small companies such as bakeries money, the Drop & Go sale offers customers who sign up during the offer period the chance to send a medium package for the price of a small one, saving them £2.45.
The sale also offers customers 25% off special delivery parcels between 1-2kg.
Eamon Price, head of mail at the Post Office, said: “Drop & Go is one of many changes taking place across the Post Office network to make it as easy as possible for customers to access our services. The summer parcels discount shows our commitment to helping small businesses and online sellers to keep down costs, enabling them to get on with running their companies.
“Drop & Go is already providing a much quicker, simpler and more effective experience for customers – and this discount goes further to helping them run a successful and profitable company.”
The Drop & Go service also means that those who sign up can drop their parcel at a fast drop counter.
The sale lasts until 27 July, and signing up as a Drop & Go customer is free.