Know about-I R C and how it works.

What are international reply coupons and how do they work?

When one writes to a stranger and requests a reply, it is considered polite to enclose a stamped self-addressed envelope. This works well when both persons live in the same country. However, if they are from different countries, the enclosed postage stamp will not be valid. The UPU solved this problem by introducing international reply coupons, exchangeable in all UPU member countries. Their value is equal to the minimum postage for a priority or unregistered airmail letter sent to a foreign country. This service is particularly popular among stamp collectors, who commonly use it to exchange philatelic information.
The UPU’s International Bureau processes approximately six million coupons each year and takes care of all accounting aspects.