A PO BOX number can be less than or more than four digit. For post office boxes, the general rule is that each box has its own ZIP+4 code.
The last four digit is often one of the following:
1. Zero plus the last three digits of the box number (eg. PO BOX 1001, Los Angeles CA 90001-0001).
2. The last four digits of the box number (eg. PO BOX 9991, Twin Peaks CA 92391-9991).
3. If the box number is less than four digits, enough zeros prepended to the front of the box number to produce a four-digit number(eg. PO BOX 1, Shreveport LA 71161-0001).
However, there is no uniform rule, the zip code plus four is for reference only, the ZIP+4 code must be looked up individually for each box in the USPS offical website.
PO BOX 422151, SAN FRANCISCO, CA 94142-2151
PO BOX 422152, SAN FRANCISCO, CA 94142-2152
PO BOX 422153, SAN FRANCISCO, CA 94142-2153
PO BOX 422154, SAN FRANCISCO, CA 94142-2154
PO BOX 422155, SAN FRANCISCO, CA 94142-2155
PO BOX 422156, SAN FRANCISCO, CA 94142-2156
PO BOX 422157, SAN FRANCISCO, CA 94142-2157
PO BOX 422158, SAN FRANCISCO, CA 94142-2158
PO BOX 422159, SAN FRANCISCO, CA 94142-2159
PO BOX 422160, SAN FRANCISCO, CA 94142-2160
PO BOX 422161, SAN FRANCISCO, CA 94142-2161
PO BOX 422162, SAN FRANCISCO, CA 94142-2162
PO BOX 422163, SAN FRANCISCO, CA 94142-2163
PO BOX 422164, SAN FRANCISCO, CA 94142-2164
PO BOX 422165, SAN FRANCISCO, CA 94142-2165
PO BOX 422166, SAN FRANCISCO, CA 94142-2166
PO BOX 422167, SAN FRANCISCO, CA 94142-2167
PO BOX 422168, SAN FRANCISCO, CA 94142-2168
PO BOX 422169, SAN FRANCISCO, CA 94142-2169
PO BOX 422170, SAN FRANCISCO, CA 94142-2170
PO BOX 422171, SAN FRANCISCO, CA 94142-2171
PO BOX 422172, SAN FRANCISCO, CA 94142-2172
PO BOX 422173, SAN FRANCISCO, CA 94142-2173
PO BOX 422174, SAN FRANCISCO, CA 94142-2174
PO BOX 422175, SAN FRANCISCO, CA 94142-2175
PO BOX 422176, SAN FRANCISCO, CA 94142-2176
PO BOX 422177, SAN FRANCISCO, CA 94142-2177
PO BOX 422178, SAN FRANCISCO, CA 94142-2178
PO BOX 422179, SAN FRANCISCO, CA 94142-2179
PO BOX 422180, SAN FRANCISCO, CA 94142-2180
PO BOX 422181, SAN FRANCISCO, CA 94142-2181
PO BOX 422182, SAN FRANCISCO, CA 94142-2182
PO BOX 422183, SAN FRANCISCO, CA 94142-2183
PO BOX 422184, SAN FRANCISCO, CA 94142-2184
PO BOX 422185, SAN FRANCISCO, CA 94142-2185
PO BOX 422186, SAN FRANCISCO, CA 94142-2186
PO BOX 422187, SAN FRANCISCO, CA 94142-2187
PO BOX 422188, SAN FRANCISCO, CA 94142-2188
PO BOX 422189, SAN FRANCISCO, CA 94142-2189
PO BOX 422190, SAN FRANCISCO, CA 94142-2190
PO BOX 422191, SAN FRANCISCO, CA 94142-2191
PO BOX 422192, SAN FRANCISCO, CA 94142-2192
PO BOX 422193, SAN FRANCISCO, CA 94142-2193
PO BOX 422194, SAN FRANCISCO, CA 94142-2194
PO BOX 422195, SAN FRANCISCO, CA 94142-2195
PO BOX 422196, SAN FRANCISCO, CA 94142-2196
PO BOX 422197, SAN FRANCISCO, CA 94142-2197
PO BOX 422198, SAN FRANCISCO, CA 94142-2198
PO BOX 422199, SAN FRANCISCO, CA 94142-2199
PO BOX 422200, SAN FRANCISCO, CA 94142-2200
PO BOX 422201, SAN FRANCISCO, CA 94142-2201
PO BOX 422202, SAN FRANCISCO, CA 94142-2202
PO BOX 422203, SAN FRANCISCO, CA 94142-2203
PO BOX 422204, SAN FRANCISCO, CA 94142-2204
PO BOX 422205, SAN FRANCISCO, CA 94142-2205
PO BOX 422206, SAN FRANCISCO, CA 94142-2206
PO BOX 422207, SAN FRANCISCO, CA 94142-2207
PO BOX 422208, SAN FRANCISCO, CA 94142-2208
PO BOX 422209, SAN FRANCISCO, CA 94142-2209
PO BOX 422210, SAN FRANCISCO, CA 94142-2210
PO BOX 422211, SAN FRANCISCO, CA 94142-2211
PO BOX 422212, SAN FRANCISCO, CA 94142-2212
PO BOX 422213, SAN FRANCISCO, CA 94142-2213
PO BOX 422214, SAN FRANCISCO, CA 94142-2214
PO BOX 422215, SAN FRANCISCO, CA 94142-2215
PO BOX 422216, SAN FRANCISCO, CA 94142-2216
PO BOX 422217, SAN FRANCISCO, CA 94142-2217
PO BOX 422218, SAN FRANCISCO, CA 94142-2218
PO BOX 422219, SAN FRANCISCO, CA 94142-2219
PO BOX 422220, SAN FRANCISCO, CA 94142-2220
PO BOX 422221, SAN FRANCISCO, CA 94142-2221
PO BOX 422222, SAN FRANCISCO, CA 94142-2222
PO BOX 422223, SAN FRANCISCO, CA 94142-2223
PO BOX 422224, SAN FRANCISCO, CA 94142-2224
PO BOX 422225, SAN FRANCISCO, CA 94142-2225
PO BOX 422226, SAN FRANCISCO, CA 94142-2226
PO BOX 422227, SAN FRANCISCO, CA 94142-2227
PO BOX 422228, SAN FRANCISCO, CA 94142-2228
PO BOX 422229, SAN FRANCISCO, CA 94142-2229
PO BOX 422230, SAN FRANCISCO, CA 94142-2230
PO BOX 422231, SAN FRANCISCO, CA 94142-2231
PO BOX 422232, SAN FRANCISCO, CA 94142-2232
PO BOX 422233, SAN FRANCISCO, CA 94142-2233
PO BOX 422234, SAN FRANCISCO, CA 94142-2234
PO BOX 422235, SAN FRANCISCO, CA 94142-2235
PO BOX 422236, SAN FRANCISCO, CA 94142-2236
PO BOX 422237, SAN FRANCISCO, CA 94142-2237
PO BOX 422238, SAN FRANCISCO, CA 94142-2238
PO BOX 422239, SAN FRANCISCO, CA 94142-2239
PO BOX 422240, SAN FRANCISCO, CA 94142-2240
PO BOX 422241, SAN FRANCISCO, CA 94142-2241
PO BOX 422242, SAN FRANCISCO, CA 94142-2242
PO BOX 422243, SAN FRANCISCO, CA 94142-2243
PO BOX 422244, SAN FRANCISCO, CA 94142-2244
PO BOX 422245, SAN FRANCISCO, CA 94142-2245
PO BOX 422246, SAN FRANCISCO, CA 94142-2246
PO BOX 422247, SAN FRANCISCO, CA 94142-2247
PO BOX 422248, SAN FRANCISCO, CA 94142-2248
PO BOX 422249, SAN FRANCISCO, CA 94142-2249
PO BOX 422250, SAN FRANCISCO, CA 94142-2250
PO BOX 422251, SAN FRANCISCO, CA 94142-2251
PO BOX 422252, SAN FRANCISCO, CA 94142-2252
PO BOX 422253, SAN FRANCISCO, CA 94142-2253
PO BOX 422254, SAN FRANCISCO, CA 94142-2254
PO BOX 422255, SAN FRANCISCO, CA 94142-2255
PO BOX 422256, SAN FRANCISCO, CA 94142-2256
PO BOX 422257, SAN FRANCISCO, CA 94142-2257
PO BOX 422258, SAN FRANCISCO, CA 94142-2258
PO BOX 422259, SAN FRANCISCO, CA 94142-2259
PO BOX 422260, SAN FRANCISCO, CA 94142-2260
PO BOX 422261, SAN FRANCISCO, CA 94142-2261
PO BOX 422262, SAN FRANCISCO, CA 94142-2262
PO BOX 422263, SAN FRANCISCO, CA 94142-2263
PO BOX 422264, SAN FRANCISCO, CA 94142-2264
PO BOX 422265, SAN FRANCISCO, CA 94142-2265
PO BOX 422266, SAN FRANCISCO, CA 94142-2266
PO BOX 422267, SAN FRANCISCO, CA 94142-2267
PO BOX 422268, SAN FRANCISCO, CA 94142-2268
PO BOX 422269, SAN FRANCISCO, CA 94142-2269
PO BOX 422270, SAN FRANCISCO, CA 94142-2270
PO BOX 422271, SAN FRANCISCO, CA 94142-2271
PO BOX 422272, SAN FRANCISCO, CA 94142-2272
PO BOX 422273, SAN FRANCISCO, CA 94142-2273
PO BOX 422274, SAN FRANCISCO, CA 94142-2274
PO BOX 422275, SAN FRANCISCO, CA 94142-2275
PO BOX 422276, SAN FRANCISCO, CA 94142-2276
PO BOX 422277, SAN FRANCISCO, CA 94142-2277
PO BOX 422278, SAN FRANCISCO, CA 94142-2278
PO BOX 422279, SAN FRANCISCO, CA 94142-2279
PO BOX 422280, SAN FRANCISCO, CA 94142-2280
PO BOX 422281, SAN FRANCISCO, CA 94142-2281
PO BOX 422282, SAN FRANCISCO, CA 94142-2282
PO BOX 422283, SAN FRANCISCO, CA 94142-2283
PO BOX 422284, SAN FRANCISCO, CA 94142-2284
PO BOX 422285, SAN FRANCISCO, CA 94142-2285
PO BOX 422286, SAN FRANCISCO, CA 94142-2286
PO BOX 422287, SAN FRANCISCO, CA 94142-2287
PO BOX 422288, SAN FRANCISCO, CA 94142-2288
PO BOX 422289, SAN FRANCISCO, CA 94142-2289
PO BOX 422290, SAN FRANCISCO, CA 94142-2290
PO BOX 422291, SAN FRANCISCO, CA 94142-2291
PO BOX 422292, SAN FRANCISCO, CA 94142-2292
PO BOX 422293, SAN FRANCISCO, CA 94142-2293
PO BOX 422294, SAN FRANCISCO, CA 94142-2294
PO BOX 422295, SAN FRANCISCO, CA 94142-2295
PO BOX 422296, SAN FRANCISCO, CA 94142-2296
PO BOX 422297, SAN FRANCISCO, CA 94142-2297
PO BOX 422298, SAN FRANCISCO, CA 94142-2298
PO BOX 422299, SAN FRANCISCO, CA 94142-2299
PO BOX 422300, SAN FRANCISCO, CA 94142-2300
PO BOX 422301, SAN FRANCISCO, CA 94142-2301
PO BOX 422302, SAN FRANCISCO, CA 94142-2302
PO BOX 422303, SAN FRANCISCO, CA 94142-2303
PO BOX 422304, SAN FRANCISCO, CA 94142-2304
PO BOX 422305, SAN FRANCISCO, CA 94142-2305
PO BOX 422306, SAN FRANCISCO, CA 94142-2306
PO BOX 422307, SAN FRANCISCO, CA 94142-2307
PO BOX 422308, SAN FRANCISCO, CA 94142-2308
PO BOX 422309, SAN FRANCISCO, CA 94142-2309
PO BOX 422310, SAN FRANCISCO, CA 94142-2310
PO BOX 422311, SAN FRANCISCO, CA 94142-2311
PO BOX 422312, SAN FRANCISCO, CA 94142-2312
PO BOX 422313, SAN FRANCISCO, CA 94142-2313
PO BOX 422314, SAN FRANCISCO, CA 94142-2314
PO BOX 422315, SAN FRANCISCO, CA 94142-2315
PO BOX 422316, SAN FRANCISCO, CA 94142-2316
PO BOX 422317, SAN FRANCISCO, CA 94142-2317
PO BOX 422318, SAN FRANCISCO, CA 94142-2318
PO BOX 422319, SAN FRANCISCO, CA 94142-2319
PO BOX 422320, SAN FRANCISCO, CA 94142-2320
PO BOX 422321, SAN FRANCISCO, CA 94142-2321
PO BOX 422322, SAN FRANCISCO, CA 94142-2322
PO BOX 422323, SAN FRANCISCO, CA 94142-2323
PO BOX 422324, SAN FRANCISCO, CA 94142-2324
PO BOX 422325, SAN FRANCISCO, CA 94142-2325
PO BOX 422326, SAN FRANCISCO, CA 94142-2326
PO BOX 422327, SAN FRANCISCO, CA 94142-2327
PO BOX 422328, SAN FRANCISCO, CA 94142-2328
PO BOX 422329, SAN FRANCISCO, CA 94142-2329
PO BOX 422330, SAN FRANCISCO, CA 94142-2330
PO BOX 422331, SAN FRANCISCO, CA 94142-2331
PO BOX 422332, SAN FRANCISCO, CA 94142-2332
PO BOX 422333, SAN FRANCISCO, CA 94142-2333
PO BOX 422334, SAN FRANCISCO, CA 94142-2334
PO BOX 422335, SAN FRANCISCO, CA 94142-2335
PO BOX 422336, SAN FRANCISCO, CA 94142-2336
PO BOX 422337, SAN FRANCISCO, CA 94142-2337
PO BOX 422338, SAN FRANCISCO, CA 94142-2338
PO BOX 422339, SAN FRANCISCO, CA 94142-2339
PO BOX 422340, SAN FRANCISCO, CA 94142-2340
PO BOX 422341, SAN FRANCISCO, CA 94142-2341
PO BOX 422342, SAN FRANCISCO, CA 94142-2342
PO BOX 422343, SAN FRANCISCO, CA 94142-2343
PO BOX 422344, SAN FRANCISCO, CA 94142-2344
PO BOX 422345, SAN FRANCISCO, CA 94142-2345
PO BOX 422346, SAN FRANCISCO, CA 94142-2346
PO BOX 422347, SAN FRANCISCO, CA 94142-2347
PO BOX 422348, SAN FRANCISCO, CA 94142-2348
PO BOX 422349, SAN FRANCISCO, CA 94142-2349
PO BOX 422350, SAN FRANCISCO, CA 94142-2350
PO BOX 422351, SAN FRANCISCO, CA 94142-2351