The use of the Information Service is subject to an agreement made with Posti. It requires the Information Service identifier and a customer-specific bar code to be printed on items sent. The use of a bar code is recommended, but not compulsory. Identifying information (such as a customer number) is provided by the customer, and the code should comply with the CODE39 bar code format. If your service level is 0, no bar code will be required. In this case, it is sufficient that you print the service number next to or under the Information Service "i" identifier.