A little about mail rates. The
Universal Postal Union (UPU)
was created in 1874 and helped standardize mail rates between countries. During the 2nd Bureau stamp era,
countries that joined the UPU set their foreign letter rate to 10 centimes per 15 grams or 5 cents per ½ ounce. This
rate remained in effect until Oct. 1, 1907, where the letter rate changed to 5 cents per
ounce and 3 cents for each additional ounce.