Automating AR cash application

Hi,

Currently all of our AR is handled manually and we are planning to automate AR cash application.We are in a situation where some of our customers send their payments referencing an invoice number and a large portion of our customers do not have an invoice number while sending their payments to the bank.Can we use lockbox functionality in SAP to auto apply the payments when we do not have an invoice number from the customer?Can we basically match on customer number and amount while applying the payments automatically?