As a box code, 2021 is used for 24 post office box locations.
Suburbs using 2021 as street code
| Suburb | Town | Province |
|---|---|---|
| Kengies | Broadacres | Gauteng |
| Kengies Ext 21 | Broadacres | Gauteng |
| Broadacres | Bryanston | Gauteng |
| Winston | Bryanston | Gauteng |
PO Boxes using 2021
| Suburb | Town | Province |
|---|---|---|
| Cobbleway Country Estate | Broadacres | Gauteng |
| Douglasdale Ext | Bryanston | Gauteng |
| Blandford Ridge | Johannesburg | Gauteng |
| Blue Heaven | Johannesburg | Gauteng |
| Brecknock | Johannesburg | Gauteng |
| Brendavere | Johannesburg | Gauteng |
| Bryanston | Johannesburg | Gauteng |
| Bryanston Ext 12 | Johannesburg | Gauteng |
| Bryanston Ext 13 | Johannesburg | Gauteng |
| Bryanston Ext 2 | Johannesburg | Gauteng |
| Bryanston Ext 4 | Johannesburg | Gauteng |
| Bryanston Ext 50 | Johannesburg | Gauteng |
| Bryanston Ext 63 | Johannesburg | Gauteng |
| Bryanston Ext 7 | Johannesburg | Gauteng |
| Craigavon | Johannesburg | Gauteng |
| Glen Nerine | Johannesburg | Gauteng |
| Leaholm | Johannesburg | Gauteng |
| Merrow Down | Johannesburg | Gauteng |
| Ornihaven | Johannesburg | Gauteng |
| Palmlands | Johannesburg | Gauteng |
| Pine Slopes | Johannesburg | Gauteng |
| Roospark | Johannesburg | Gauteng |
| Salsfred | Johannesburg | Gauteng |
| Hurlingham Manor | Saxonwold | Gauteng |