Australia Post has announced that it will buy a majority shareholding in MailPlus.MailPlus is a company that provides mail collection, mail lodgement, parcel collection and banking services for businesses.Why is Australia Post making this investment? Australia Post says that the investment will mean AP will be able to extend its support for start-ups and small businesses to make it easier for them to complete everyday jobs, including interacting with the post office network.We'll wait and see what plans Australia Post might have to integrate MailPlus into the business, perhaps under the Star Track umbrella.