The DOP customer ID in post office refers to the CIF ID printed on the first page of the passbook. It is a 9-digit number that is required for registering for DOP internet banking. The account ID, on the other hand, is the SB account number printed on the first page of the passbook. To activate DOP internet banking, customers need to visit their home branch, fill the pre-printed application form, and submit it with the required documents. Once the request is processed successfully, an SMS alert will be delivered to the registered mobile number within 48 hours.