Post packs as disributed by Australia Post are one of the most favoured means of collecting mint stamps.
They come in a protective folder with information pertaining to their history and source,
This one covering our friends the dolphins.
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2 m (4 ft) and 40 kg (90 lb), up to 9.5 m (30 ft) and 10 tonnes (9.8 LT; 11 ST) (the Orca or Killer Whale). They are found worldwide, mostly in the shallower seas of the continental shelves and are carnivores, mostly eating fish and squid. Dolphins evolved about ten million years ago, during the Miocene. Dolphins are among the most intelligent animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture.
*All historical information taken from Wikipedia for educational purposes only