Effective January 4, 2010, return addresses are required on all outbound international mail - regardless of service used.  The new requirement is being established in response to changes in Universal Postal Union (UPU) regulations.  It specifies that mailpieces must bear a complete return address in the country of origin (where you pay postage).  In other words, if mailed through the USPS, return must be a US address (See USPS Regulation 122.23).  If mailed direct through Canada Post, return must be Canadian.  Further, it’s recommended that the destination country name be on the last line in capital letters.