This is an optional api that can be use to retrieve USPS Electronic Return Reciepts for Certified Mail, Priority Mail and Priority Express Mail." + "This call is for API customers that need to associate a unique id to each mail recipient that will be used to identify a specific mail piece for pulling electronic return reciepts." + " In order to use this feature your uploaded address list must contain column with the heading of c2m_uniqueid and each address must have a unique ID associated with it.