As a box code, 4021 is used for 6 post office box locations.
PO Boxes using 4021
| Suburb | Town | Province |
|---|---|---|
| Ilala Ridge | Durban North | KwaZulu-Natal |
| Izinga Ridge | Durban North | KwaZulu-Natal |
| Prestondale | Umhlanga Rocks | KwaZulu-Natal |
| Somerset Park | Umhlanga Rocks | KwaZulu-Natal |
| The Square | Umhlanga Rocks | KwaZulu-Natal |
| Umhlanga Manors | Umhlanga Rocks | KwaZulu-Natal |