| N | Non Postal Community Name: Former Postal Facility |
| P | Post Office: An official post office branch. |
| U | Urbanization: A postal designation specific to Puerto Rico. |
| B | Branch: A postal facility that is not the main post office and is outside the corporate limits of a city. |
| A | Airport Mail Facility: Facilities through which US mail is flown in and out of a city. |
| C | Community Post Office: a contract postal unit providing mail services to small communities. |
| S | Station: A post office that is not the main office for a city but is in corporate city limits. |
| K | Bulk Mail Center: Centers that handle bulk mail. Typically commercial, business and advertising mail. |