Effective July 6, 1851, mail was exchanged between the United States and the Maritime Provinces of New Brunswick, Nova Scotia, and Prince Edward Island pursuant to a postal agreement. The agreement provided that letters would be exchanged at 10 cents (6 pence). Letters to and from California and Oregon (over 3,000 miles from the exchange office) were charged 15 cents (9 pence). The agreement was subsequently modified to provide for a "line office rate" of 2 cents (1 pence) for letters between adjacent exchange offices not more than 5 miles apart.
Mail between the US and New Brunswick was charged a uniform rate of 10 cents beginning in August 1864, following the elimination of the 10 cent US domestic rate for distances over 3,000 miles. However, the rate between California and Nova Scotia and Prince Edward Island remained at 15 cents through 1868.
In 1868, after New Brunswick and Nova Scotia Confederated with Canada East, and Canada West, to form the Dominion of Canada, the treaty rate was reduced to 6¢ (4 pence) for prepaid letters, regardless of distance. The rate for unpaid letters remained at 10¢.
Pursuant to the treaty, letters could be paid or unpaid; however, partial payment was not recognized. Additionally, there was no division or allocation of the treaty rates. The country which collected the payment of the postage kept the entire amount.
The 10¢ Treaty Rate
The 15¢ Treaty Rate For Distances Of More Than 3,000 Miles From the Exchange Office
The 6¢ Treaty Rate Effective 1868
Printed Matter Rates
Pursuant to the postal agreement, printed matter was to be paid to the lines of the origin country at the domestic printed matter rate. Postage from the border to destination would be collected from the recipient, again at the domestic printed matter rate.