| Porter | S. L. | Williams 1590-1-2, Narrogin | SP7 and 45C, 28A | 1962 |
| Porter | T. R. & M. A. | Linton, Highbury | 1SR and 35D, 58F | 1962 |
| Porter | V. E. | Locs. 7600, 3544-5, 7850, Kojonup | V4P and 32B, 52F | 1962 |
| Porter | W. A. | Mooney Vale, Coolup | 5FP | 1924 |
| Porter | W. A. & A. M. | Mooney Vale, Coolup | 5FP | 1912 |
| Porter | Wm. | Model Dairy, Abernethy Street, Belmont | W2P | 1912 |
| Porter & Co. | F. A. | Riverside, Ajana | P9L and 32C, 26A | 1962 |
| Porter & Lodge | F. A. & C. | Victoria Loc. 4668, Ajana | P9L | 1924 |
| Porter & Sons | J. H. | Koroitdale, Coomberdale | 4PO and 13B, 58F | 1962 |
| Porter Bros. | - | Rocky Vale, Narrogin | PB7 | 1912 |
| Porter Bros. | - | Rocky Vale, Narrogin | PB7 | 1924 |
| Portner | J. F. | Blocks 20400/55 and 10429/74, East Wagin | JP4 | 1912 |
| Portner | J. F. | Blocks 20400/55 & 10429/74, Wagin East | JP4 | 1924 |
| Posa | M. | Loc. 383, Jilbadji, Southern Cross | 1MP and 22B, 71E | 1962 |
| Posselt | E. | Group 45, Locs. 360-1, Serpentine | E7P | 1962 |
| Posselt & Co. | R. J. | Glenronda, Glenbrook, Drumin, Northam | R4P and 84D, 58F | 1962 |
| Postans | David | Hope Valley, Rockingham | DP7 | 1912 |
| Postans | David | Hope Valley, Rockingham | DP7 | 1924 |
| Postans | Fred | Keysbrook, Serpentine | F0P | 1912 |
| Postans | Fred | Hope Valley, Rockingham, Keysbrook, Serpentine | F0P | 1924 |
| Postans | Grace E. | Hope Valley, Rockingham | GP7 | 1912 |
| Postans | Grace E. | Hope Valley, Rockingham | GP7 | 1924 |
| Postans | Harriet | Coronation, Hope Valley | 2HP | 1912 |
| Postans | Harriett | Coronation, Hope Valley | 2HP | 1924 |
| Postans | Maud Mary | Marrinup, via Pinjarra | M8P | 1924 |
| Postmaster General's Department | - | throughout the state | T1D | 1924 |
| Postmaster Generals Department | - | Throughout the State | T1D | 1912 |
| Pott | Hannah Mary | Hillside, Kellerberrin | 8SP | 1924 |
| Potter | A. G. W. | Stirling Park, Kendenup | PU7 and 18D, 103E | 1962 |
| Potter | F. John | Commonage No. 405A, Albany | ZZ6 | 1912 |
| Potter | F. John | Commonage No. 405A, Albany | ZZ6 | 1924 |
| Potter | J. | Loc. 506, Denmark | P9E | 1962 |
| Potter | J. L. | 1649, Forest Grove | L0P | 1962 |
| Potter | K. J. | Springfield, Forest Grove | 7KP | 1962 |
| Potter | N. H. & L. W. | Wanderberry, Walebing, Via Moora | 4NP and 46C, 110A | 1962 |
| Potter | N. W. | Jam Hill, Woodanilling | N6P and 28C, 80E | 1962 |
| Potter & Co. | S. F. | Delamere, Boyup Brook | ZZ6 | 1962 |
| Potter & Sons | J. W. & G. M. M. | Nelson 12311-6 inclusive and 12084, Northcliffe | 5JP and 16C, 19A | 1962 |
| Potthoff & Sons | W. | Ekamurra, Kondinin | X5P and 3C, 46A | 1962 |
| Pottle | Wm. | Blocks 285 and461 | W4P | 1912 |
| Pottle | Wm. | Blocks, 285 & 461, Narrogin | W4P | 1924 |
| Potts | A. H. | 6 Banford Street, Albany | HP2 and 3B, 14E | 1962 |
| Potts | A. J. | Water Vale, West Pingelly | C2D and 20B, 102E | 1962 |
| Potts | A. J. & H. A. | Tally Ho, Ruabon | 4VE and 40B, 8E | 1962 |
| Potts | A. W. | Marleyup, Kojonup | FH6 | 1924 |
| Potts | C. E. | Auburn, Pingelly | C1P | 1912 |
| Potts | C. E. | Auburn, Pingelly | C1P | 1924 |
| Potts | C. H. | Ninghan 2340, 4000, 4016, Bencubbin and Byford | P8C and 51F, 120B | 1962 |
| Potts | C. W. | Auburn Farm, West Pingelly | FX1 and 15B, 102E | 1962 |
| Potts | C. W. & L. M. | Auburn Farm, West Pingelly | C1P and 16B, 21A | 1962 |
