In 1955 the Royal Government of Bhutan introduced a regular dispatch of mail at intervals of five days, while the mail system was expanded to include personal mail as well. The fiscal revenue stamps, which had been introduced the year before, had to be used as a token of payment for the services, except for mail to H.M. the King, which was free of charge. This revised mail runner system with the use of fiscals as postage is often referred to as the Dzong Dak system (dak means ‘post’ or ‘mail’ in Hindi). Mail was for delivery within Bhutan only as these postal fiscals had no validity outside the kingdom.
Some letters for abroad, however, were carried by courier to Yatung or Phari in Tibet or post offices in India for further forwarding by regular mail. Both India and China maintained post offices in Yatung, where their respective stamps were affixed for onward carriage. Most of the known covers using this route were destined for the Bhutanese representation in Kalimpong, India, known as Bhutan House.