Topic summary
International mail
Extracted from the Wikipedia article Universal Postal Union.
Further developments
Toward the end of the 19th century, the UPU issued rules concerning stamp design, intended to ensure maximum efficiency in handling international mail. One rule specified that stamp values be given in numerals, as denominations written out in letters were not universally comprehensible. Another required member nations to use the same colors on their stamps issued for post cards (green), normal letters (red) and international mail (blue), a system that remained in use for several decades.