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 21, SOLON, IA 52333-0021
PO BOX 22, SOLON, IA 52333-0022
PO BOX 23, SOLON, IA 52333-0023
PO BOX 24, SOLON, IA 52333-0024
PO BOX 25, SOLON, IA 52333-0025
PO BOX 26, SOLON, IA 52333-0026
PO BOX 27, SOLON, IA 52333-0027
PO BOX 28, SOLON, IA 52333-0028
PO BOX 29, SOLON, IA 52333-0029
PO BOX 30, SOLON, IA 52333-0030
PO BOX 31, SOLON, IA 52333-0031
PO BOX 32, SOLON, IA 52333-0032
PO BOX 33, SOLON, IA 52333-0033
PO BOX 34, SOLON, IA 52333-0034
PO BOX 35, SOLON, IA 52333-0035
PO BOX 36, SOLON, IA 52333-0036
PO BOX 37, SOLON, IA 52333-0037
PO BOX 38, SOLON, IA 52333-0038
PO BOX 39, SOLON, IA 52333-0039
PO BOX 40, SOLON, IA 52333-0040
PO BOX 41, SOLON, IA 52333-0041
PO BOX 42, SOLON, IA 52333-0042
PO BOX 43, SOLON, IA 52333-0043
PO BOX 44, SOLON, IA 52333-0044
PO BOX 45, SOLON, IA 52333-0045
PO BOX 46, SOLON, IA 52333-0046
PO BOX 47, SOLON, IA 52333-0047
PO BOX 48, SOLON, IA 52333-0048
PO BOX 49, SOLON, IA 52333-0049
PO BOX 50, SOLON, IA 52333-0050
PO BOX 51, SOLON, IA 52333-0051
PO BOX 52, SOLON, IA 52333-0052
PO BOX 53, SOLON, IA 52333-0053
PO BOX 54, SOLON, IA 52333-0054
PO BOX 55, SOLON, IA 52333-0055
PO BOX 56, SOLON, IA 52333-0056
PO BOX 57, SOLON, IA 52333-0057
PO BOX 58, SOLON, IA 52333-0058
PO BOX 59, SOLON, IA 52333-0059
PO BOX 60, SOLON, IA 52333-0060
PO BOX 61, SOLON, IA 52333-0061
PO BOX 62, SOLON, IA 52333-0062
PO BOX 63, SOLON, IA 52333-0063
PO BOX 64, SOLON, IA 52333-0064
PO BOX 65, SOLON, IA 52333-0065
PO BOX 66, SOLON, IA 52333-0066
PO BOX 67, SOLON, IA 52333-0067
PO BOX 68, SOLON, IA 52333-0068
PO BOX 69, SOLON, IA 52333-0069
PO BOX 70, SOLON, IA 52333-0070
PO BOX 71, SOLON, IA 52333-0071
PO BOX 72, SOLON, IA 52333-0072
PO BOX 73, SOLON, IA 52333-0073
PO BOX 74, SOLON, IA 52333-0074
PO BOX 75, SOLON, IA 52333-0075
PO BOX 76, SOLON, IA 52333-0076
PO BOX 77, SOLON, IA 52333-0077
PO BOX 78, SOLON, IA 52333-0078
PO BOX 79, SOLON, IA 52333-0079
PO BOX 80, SOLON, IA 52333-0080
PO BOX 81, SOLON, IA 52333-0081
PO BOX 82, SOLON, IA 52333-0082
PO BOX 83, SOLON, IA 52333-0083
PO BOX 84, SOLON, IA 52333-0084
PO BOX 85, SOLON, IA 52333-0085
PO BOX 86, SOLON, IA 52333-0086
PO BOX 87, SOLON, IA 52333-0087
PO BOX 88, SOLON, IA 52333-0088
PO BOX 89, SOLON, IA 52333-0089
PO BOX 90, SOLON, IA 52333-0090
PO BOX 91, SOLON, IA 52333-0091
PO BOX 92, SOLON, IA 52333-0092
PO BOX 93, SOLON, IA 52333-0093
PO BOX 94, SOLON, IA 52333-0094
PO BOX 95, SOLON, IA 52333-0095
PO BOX 96, SOLON, IA 52333-0096
PO BOX 97, SOLON, IA 52333-0097
PO BOX 98, SOLON, IA 52333-0098
PO BOX 99, SOLON, IA 52333-0099
PO BOX 100, SOLON, IA 52333-0100
PO BOX 101, SOLON, IA 52333-0101
PO BOX 102, SOLON, IA 52333-0102
PO BOX 103, SOLON, IA 52333-0103
PO BOX 104, SOLON, IA 52333-0104
PO BOX 105, SOLON, IA 52333-0105
PO BOX 106, SOLON, IA 52333-0106
PO BOX 107, SOLON, IA 52333-0107
PO BOX 108, SOLON, IA 52333-0108
PO BOX 109, SOLON, IA 52333-0109
PO BOX 110, SOLON, IA 52333-0110
PO BOX 111, SOLON, IA 52333-0111
PO BOX 112, SOLON, IA 52333-0112
PO BOX 113, SOLON, IA 52333-0113
PO BOX 114, SOLON, IA 52333-0114
PO BOX 115, SOLON, IA 52333-0115
PO BOX 116, SOLON, IA 52333-0116
PO BOX 117, SOLON, IA 52333-0117
PO BOX 118, SOLON, IA 52333-0118
PO BOX 119, SOLON, IA 52333-0119
PO BOX 120, SOLON, IA 52333-0120
PO BOX 121, SOLON, IA 52333-0121
PO BOX 122, SOLON, IA 52333-0122
PO BOX 123, SOLON, IA 52333-0123
PO BOX 124, SOLON, IA 52333-0124
PO BOX 125, SOLON, IA 52333-0125
PO BOX 126, SOLON, IA 52333-0126
PO BOX 127, SOLON, IA 52333-0127
PO BOX 128, SOLON, IA 52333-0128
PO BOX 129, SOLON, IA 52333-0129
PO BOX 130, SOLON, IA 52333-0130
PO BOX 131, SOLON, IA 52333-0131
PO BOX 132, SOLON, IA 52333-0132
PO BOX 133, SOLON, IA 52333-0133
PO BOX 134, SOLON, IA 52333-0134
PO BOX 135, SOLON, IA 52333-0135
PO BOX 136, SOLON, IA 52333-0136
PO BOX 137, SOLON, IA 52333-0137
PO BOX 138, SOLON, IA 52333-0138
PO BOX 139, SOLON, IA 52333-0139
PO BOX 140, SOLON, IA 52333-0140
PO BOX 141, SOLON, IA 52333-0141
PO BOX 142, SOLON, IA 52333-0142
PO BOX 143, SOLON, IA 52333-0143
PO BOX 144, SOLON, IA 52333-0144
PO BOX 145, SOLON, IA 52333-0145
PO BOX 146, SOLON, IA 52333-0146
PO BOX 147, SOLON, IA 52333-0147
PO BOX 148, SOLON, IA 52333-0148
PO BOX 149, SOLON, IA 52333-0149
PO BOX 150, SOLON, IA 52333-0150
PO BOX 151, SOLON, IA 52333-0151
PO BOX 152, SOLON, IA 52333-0152
PO BOX 153, SOLON, IA 52333-0153
PO BOX 154, SOLON, IA 52333-0154
PO BOX 155, SOLON, IA 52333-0155
PO BOX 156, SOLON, IA 52333-0156
PO BOX 157, SOLON, IA 52333-0157
PO BOX 158, SOLON, IA 52333-0158
PO BOX 159, SOLON, IA 52333-0159
PO BOX 160, SOLON, IA 52333-0160
PO BOX 161, SOLON, IA 52333-0161
PO BOX 162, SOLON, IA 52333-0162
PO BOX 163, SOLON, IA 52333-0163
PO BOX 164, SOLON, IA 52333-0164
PO BOX 165, SOLON, IA 52333-0165
PO BOX 166, SOLON, IA 52333-0166
PO BOX 167, SOLON, IA 52333-0167
PO BOX 168, SOLON, IA 52333-0168
PO BOX 169, SOLON, IA 52333-0169
PO BOX 170, SOLON, IA 52333-0170
PO BOX 171, SOLON, IA 52333-0171
PO BOX 172, SOLON, IA 52333-0172
PO BOX 173, SOLON, IA 52333-0173
PO BOX 174, SOLON, IA 52333-0174
PO BOX 175, SOLON, IA 52333-0175
PO BOX 176, SOLON, IA 52333-0176
PO BOX 177, SOLON, IA 52333-0177
PO BOX 178, SOLON, IA 52333-0178
PO BOX 179, SOLON, IA 52333-0179
PO BOX 180, SOLON, IA 52333-0180
PO BOX 181, SOLON, IA 52333-0181
PO BOX 182, SOLON, IA 52333-0182
PO BOX 183, SOLON, IA 52333-0183
PO BOX 184, SOLON, IA 52333-0184
PO BOX 185, SOLON, IA 52333-0185
PO BOX 186, SOLON, IA 52333-0186
PO BOX 187, SOLON, IA 52333-0187
PO BOX 188, SOLON, IA 52333-0188
PO BOX 189, SOLON, IA 52333-0189
PO BOX 190, SOLON, IA 52333-0190
PO BOX 191, SOLON, IA 52333-0191
PO BOX 192, SOLON, IA 52333-0192
PO BOX 193, SOLON, IA 52333-0193
PO BOX 194, SOLON, IA 52333-0194
PO BOX 195, SOLON, IA 52333-0195
PO BOX 196, SOLON, IA 52333-0196
PO BOX 197, SOLON, IA 52333-0197
PO BOX 198, SOLON, IA 52333-0198
PO BOX 199, SOLON, IA 52333-0199
PO BOX 200, SOLON, IA 52333-0200
PO BOX 201, SOLON, IA 52333-0201
PO BOX 202, SOLON, IA 52333-0202
PO BOX 203, SOLON, IA 52333-0203
PO BOX 204, SOLON, IA 52333-0204
PO BOX 205, SOLON, IA 52333-0205
PO BOX 206, SOLON, IA 52333-0206
PO BOX 207, SOLON, IA 52333-0207
PO BOX 208, SOLON, IA 52333-0208
PO BOX 209, SOLON, IA 52333-0209
PO BOX 210, SOLON, IA 52333-0210
PO BOX 211, SOLON, IA 52333-0211
PO BOX 212, SOLON, IA 52333-0212
PO BOX 213, SOLON, IA 52333-0213
PO BOX 214, SOLON, IA 52333-0214
PO BOX 215, SOLON, IA 52333-0215
PO BOX 216, SOLON, IA 52333-0216
PO BOX 217, SOLON, IA 52333-0217
PO BOX 218, SOLON, IA 52333-0218
PO BOX 219, SOLON, IA 52333-0219
PO BOX 220, SOLON, IA 52333-0220
PO BOX 221, SOLON, IA 52333-0221