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 1, DOW CITY, IA 51528-0001
PO BOX 2, DOW CITY, IA 51528-0002
PO BOX 3, DOW CITY, IA 51528-0003
PO BOX 4, DOW CITY, IA 51528-0004
PO BOX 5, DOW CITY, IA 51528-0005
PO BOX 6, DOW CITY, IA 51528-0006
PO BOX 7, DOW CITY, IA 51528-0007
PO BOX 8, DOW CITY, IA 51528-0008
PO BOX 9, DOW CITY, IA 51528-0009
PO BOX 10, DOW CITY, IA 51528-0010
PO BOX 11, DOW CITY, IA 51528-0011
PO BOX 12, DOW CITY, IA 51528-0012
PO BOX 13, DOW CITY, IA 51528-0013
PO BOX 14, DOW CITY, IA 51528-0014
PO BOX 15, DOW CITY, IA 51528-0015
PO BOX 16, DOW CITY, IA 51528-0016
PO BOX 17, DOW CITY, IA 51528-0017
PO BOX 18, DOW CITY, IA 51528-0018
PO BOX 19, DOW CITY, IA 51528-0019
PO BOX 20, DOW CITY, IA 51528-0020
PO BOX 21, DOW CITY, IA 51528-0021
PO BOX 22, DOW CITY, IA 51528-0022
PO BOX 23, DOW CITY, IA 51528-0023
PO BOX 24, DOW CITY, IA 51528-0024
PO BOX 25, DOW CITY, IA 51528-0025
PO BOX 26, DOW CITY, IA 51528-0026
PO BOX 27, DOW CITY, IA 51528-0027
PO BOX 28, DOW CITY, IA 51528-0028
PO BOX 29, DOW CITY, IA 51528-0029
PO BOX 30, DOW CITY, IA 51528-0030
PO BOX 31, DOW CITY, IA 51528-0031
PO BOX 32, DOW CITY, IA 51528-0032
PO BOX 33, DOW CITY, IA 51528-0033
PO BOX 34, DOW CITY, IA 51528-0034
PO BOX 35, DOW CITY, IA 51528-0035
PO BOX 36, DOW CITY, IA 51528-0036
PO BOX 37, DOW CITY, IA 51528-0037
PO BOX 38, DOW CITY, IA 51528-0038
PO BOX 39, DOW CITY, IA 51528-0039
PO BOX 40, DOW CITY, IA 51528-0040
PO BOX 41, DOW CITY, IA 51528-0041
PO BOX 42, DOW CITY, IA 51528-0042
PO BOX 43, DOW CITY, IA 51528-0043
PO BOX 44, DOW CITY, IA 51528-0044
PO BOX 45, DOW CITY, IA 51528-0045
PO BOX 46, DOW CITY, IA 51528-0046
PO BOX 47, DOW CITY, IA 51528-0047
PO BOX 48, DOW CITY, IA 51528-0048
PO BOX 49, DOW CITY, IA 51528-0049
PO BOX 50, DOW CITY, IA 51528-0050
PO BOX 51, DOW CITY, IA 51528-0051
PO BOX 52, DOW CITY, IA 51528-0052
PO BOX 53, DOW CITY, IA 51528-0053
PO BOX 54, DOW CITY, IA 51528-0054
PO BOX 55, DOW CITY, IA 51528-0055
PO BOX 56, DOW CITY, IA 51528-0056
PO BOX 57, DOW CITY, IA 51528-0057
PO BOX 58, DOW CITY, IA 51528-0058
PO BOX 59, DOW CITY, IA 51528-0059
PO BOX 60, DOW CITY, IA 51528-0060
PO BOX 61, DOW CITY, IA 51528-0061
PO BOX 62, DOW CITY, IA 51528-0062
PO BOX 63, DOW CITY, IA 51528-0063
PO BOX 64, DOW CITY, IA 51528-0064
PO BOX 65, DOW CITY, IA 51528-0065
PO BOX 66, DOW CITY, IA 51528-0066
PO BOX 67, DOW CITY, IA 51528-0067
PO BOX 68, DOW CITY, IA 51528-0068
PO BOX 69, DOW CITY, IA 51528-0069
PO BOX 70, DOW CITY, IA 51528-0070
PO BOX 71, DOW CITY, IA 51528-0071
PO BOX 72, DOW CITY, IA 51528-0072
PO BOX 73, DOW CITY, IA 51528-0073
PO BOX 74, DOW CITY, IA 51528-0074
PO BOX 75, DOW CITY, IA 51528-0075
PO BOX 76, DOW CITY, IA 51528-0076
PO BOX 77, DOW CITY, IA 51528-0077
PO BOX 78, DOW CITY, IA 51528-0078
PO BOX 79, DOW CITY, IA 51528-0079
PO BOX 80, DOW CITY, IA 51528-0080
PO BOX 81, DOW CITY, IA 51528-0081
PO BOX 82, DOW CITY, IA 51528-0082
PO BOX 83, DOW CITY, IA 51528-0083
PO BOX 84, DOW CITY, IA 51528-0084
PO BOX 85, DOW CITY, IA 51528-0085
PO BOX 86, DOW CITY, IA 51528-0086
PO BOX 87, DOW CITY, IA 51528-0087
PO BOX 88, DOW CITY, IA 51528-0088
PO BOX 89, DOW CITY, IA 51528-0089
PO BOX 90, DOW CITY, IA 51528-0090
PO BOX 91, DOW CITY, IA 51528-0091
PO BOX 92, DOW CITY, IA 51528-0092
PO BOX 93, DOW CITY, IA 51528-0093
PO BOX 94, DOW CITY, IA 51528-0094
PO BOX 95, DOW CITY, IA 51528-0095
PO BOX 96, DOW CITY, IA 51528-0096
PO BOX 97, DOW CITY, IA 51528-0097
PO BOX 98, DOW CITY, IA 51528-0098
PO BOX 99, DOW CITY, IA 51528-0099
PO BOX 100, DOW CITY, IA 51528-0100
PO BOX 101, DOW CITY, IA 51528-0101
PO BOX 102, DOW CITY, IA 51528-0102
PO BOX 103, DOW CITY, IA 51528-0103
PO BOX 104, DOW CITY, IA 51528-0104
PO BOX 105, DOW CITY, IA 51528-0105
PO BOX 106, DOW CITY, IA 51528-0106
PO BOX 107, DOW CITY, IA 51528-0107
PO BOX 108, DOW CITY, IA 51528-0108
PO BOX 109, DOW CITY, IA 51528-0109
PO BOX 110, DOW CITY, IA 51528-0110
PO BOX 111, DOW CITY, IA 51528-0111
PO BOX 112, DOW CITY, IA 51528-0112
PO BOX 113, DOW CITY, IA 51528-0113
PO BOX 114, DOW CITY, IA 51528-0114
PO BOX 115, DOW CITY, IA 51528-0115
PO BOX 116, DOW CITY, IA 51528-0116
PO BOX 117, DOW CITY, IA 51528-0117
PO BOX 118, DOW CITY, IA 51528-0118
PO BOX 119, DOW CITY, IA 51528-0119
PO BOX 120, DOW CITY, IA 51528-0120
PO BOX 121, DOW CITY, IA 51528-0121
PO BOX 122, DOW CITY, IA 51528-0122
PO BOX 123, DOW CITY, IA 51528-0123
PO BOX 124, DOW CITY, IA 51528-0124
PO BOX 125, DOW CITY, IA 51528-0125
PO BOX 126, DOW CITY, IA 51528-0126
PO BOX 127, DOW CITY, IA 51528-0127
PO BOX 128, DOW CITY, IA 51528-0128
PO BOX 129, DOW CITY, IA 51528-0129
PO BOX 130, DOW CITY, IA 51528-0130
PO BOX 131, DOW CITY, IA 51528-0131
PO BOX 132, DOW CITY, IA 51528-0132
PO BOX 133, DOW CITY, IA 51528-0133
PO BOX 134, DOW CITY, IA 51528-0134
PO BOX 135, DOW CITY, IA 51528-0135
PO BOX 136, DOW CITY, IA 51528-0136
PO BOX 137, DOW CITY, IA 51528-0137
PO BOX 138, DOW CITY, IA 51528-0138
PO BOX 139, DOW CITY, IA 51528-0139
PO BOX 140, DOW CITY, IA 51528-0140
PO BOX 141, DOW CITY, IA 51528-0141
PO BOX 142, DOW CITY, IA 51528-0142
PO BOX 143, DOW CITY, IA 51528-0143
PO BOX 144, DOW CITY, IA 51528-0144
PO BOX 145, DOW CITY, IA 51528-0145
PO BOX 146, DOW CITY, IA 51528-0146
PO BOX 147, DOW CITY, IA 51528-0147
PO BOX 148, DOW CITY, IA 51528-0148
PO BOX 149, DOW CITY, IA 51528-0149
PO BOX 150, DOW CITY, IA 51528-0150
PO BOX 151, DOW CITY, IA 51528-0151
PO BOX 152, DOW CITY, IA 51528-0152
PO BOX 153, DOW CITY, IA 51528-0153
PO BOX 154, DOW CITY, IA 51528-0154
PO BOX 155, DOW CITY, IA 51528-0155
PO BOX 156, DOW CITY, IA 51528-0156
PO BOX 157, DOW CITY, IA 51528-0157
PO BOX 158, DOW CITY, IA 51528-0158
PO BOX 159, DOW CITY, IA 51528-0159
PO BOX 160, DOW CITY, IA 51528-0160
PO BOX 161, DOW CITY, IA 51528-0161
PO BOX 162, DOW CITY, IA 51528-0162
PO BOX 163, DOW CITY, IA 51528-0163
PO BOX 164, DOW CITY, IA 51528-0164
PO BOX 165, DOW CITY, IA 51528-0165
PO BOX 166, DOW CITY, IA 51528-0166
PO BOX 167, DOW CITY, IA 51528-0167
PO BOX 168, DOW CITY, IA 51528-0168
PO BOX 169, DOW CITY, IA 51528-0169
PO BOX 170, DOW CITY, IA 51528-0170
PO BOX 171, DOW CITY, IA 51528-0171
PO BOX 172, DOW CITY, IA 51528-0172
PO BOX 173, DOW CITY, IA 51528-0173
PO BOX 174, DOW CITY, IA 51528-0174
PO BOX 175, DOW CITY, IA 51528-0175
PO BOX 176, DOW CITY, IA 51528-0176
PO BOX 177, DOW CITY, IA 51528-0177
PO BOX 178, DOW CITY, IA 51528-0178
PO BOX 179, DOW CITY, IA 51528-0179
PO BOX 180, DOW CITY, IA 51528-0180
PO BOX 181, DOW CITY, IA 51528-0181
PO BOX 182, DOW CITY, IA 51528-0182
PO BOX 183, DOW CITY, IA 51528-0183
PO BOX 184, DOW CITY, IA 51528-0184
PO BOX 185, DOW CITY, IA 51528-0185
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