When using Electronic Return Receipt (ERR) your system prompts you to enter a customer reference number. You can use the customer reference to identify the mail piece recipient in any way you choose: by name, by a unique customer ID, by invoice number, and so on.
The customer reference can be up to 14 alphanumeric characters long and is included with the mail piece transaction data your system uploads. This feature greatly enhances mail piece tracking by linking the reference number to the package ID (tracking number).