Shipping diapers by lettermail in Canada can save on shipping costs, but does not include insurance or delivery confirmation. (thinking-about-cloth-diapers.com)
When I only purchase a single diaper at a time, I love the option of lettermail to help me save money. (thinking-about-cloth-diapers.com)
For a couple of years, Canada's had «permanent» postage stamps, whereby instead of printing a fixed value in cents on the regular lettermail stamp there is simply the letter «P» for permanent. (money.stackexchange.com)