| Abbreviation | Definition |
|---|---|
| CL | Chile |
| CM | Cameroon |
| CMA | Commercial Mailing Agent |
| CMRA | Commercial Mail Receiving Agency |
| CMRRR | Certified Mail, Return Receipt Required |
| CMRS | Computerized Meter Resetting System |
| CN | China |
| CO | Colombia |
| COA | Change Of Address |
| COD | Cash On Delivery |
| CODES | Computerized On-site Data Entry System |
| COR | Contracting Officer Representative |
| COSC | Computer Operations Service Center |
| CP | Carte Postale |
| CP | Colis Postaux (Parcel Post) |
| CPO | Community Post Office |
| CPP | Centralized Postage Payment System |
| CR | Carrier Route |
| CR | Costa Rica |
| CRES | Crescent |