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, SABULA, IA 52070-0021
PO BOX 22, SABULA, IA 52070-0022
PO BOX 23, SABULA, IA 52070-0023
PO BOX 24, SABULA, IA 52070-0024
PO BOX 25, SABULA, IA 52070-0025
PO BOX 26, SABULA, IA 52070-0026
PO BOX 27, SABULA, IA 52070-0027
PO BOX 28, SABULA, IA 52070-0028
PO BOX 29, SABULA, IA 52070-0029
PO BOX 30, SABULA, IA 52070-0030
PO BOX 31, SABULA, IA 52070-0031
PO BOX 32, SABULA, IA 52070-0032
PO BOX 33, SABULA, IA 52070-0033
PO BOX 34, SABULA, IA 52070-0034
PO BOX 35, SABULA, IA 52070-0035
PO BOX 36, SABULA, IA 52070-0036
PO BOX 37, SABULA, IA 52070-0037
PO BOX 38, SABULA, IA 52070-0038
PO BOX 39, SABULA, IA 52070-0039
PO BOX 40, SABULA, IA 52070-0040
PO BOX 41, SABULA, IA 52070-0041
PO BOX 42, SABULA, IA 52070-0042
PO BOX 43, SABULA, IA 52070-0043
PO BOX 44, SABULA, IA 52070-0044
PO BOX 45, SABULA, IA 52070-0045
PO BOX 46, SABULA, IA 52070-0046
PO BOX 47, SABULA, IA 52070-0047
PO BOX 48, SABULA, IA 52070-0048
PO BOX 49, SABULA, IA 52070-0049
PO BOX 50, SABULA, IA 52070-0050
PO BOX 51, SABULA, IA 52070-0051
PO BOX 52, SABULA, IA 52070-0052
PO BOX 53, SABULA, IA 52070-0053
PO BOX 54, SABULA, IA 52070-0054
PO BOX 55, SABULA, IA 52070-0055
PO BOX 56, SABULA, IA 52070-0056
PO BOX 57, SABULA, IA 52070-0057
PO BOX 58, SABULA, IA 52070-0058
PO BOX 59, SABULA, IA 52070-0059
PO BOX 60, SABULA, IA 52070-0060
PO BOX 61, SABULA, IA 52070-0061
PO BOX 62, SABULA, IA 52070-0062
PO BOX 63, SABULA, IA 52070-0063
PO BOX 64, SABULA, IA 52070-0064
PO BOX 65, SABULA, IA 52070-0065
PO BOX 66, SABULA, IA 52070-0066
PO BOX 67, SABULA, IA 52070-0067
PO BOX 68, SABULA, IA 52070-0068
PO BOX 69, SABULA, IA 52070-0069
PO BOX 70, SABULA, IA 52070-0070
PO BOX 71, SABULA, IA 52070-0071
PO BOX 72, SABULA, IA 52070-0072
PO BOX 73, SABULA, IA 52070-0073
PO BOX 74, SABULA, IA 52070-0074
PO BOX 75, SABULA, IA 52070-0075
PO BOX 76, SABULA, IA 52070-0076
PO BOX 77, SABULA, IA 52070-0077
PO BOX 78, SABULA, IA 52070-0078
PO BOX 79, SABULA, IA 52070-0079
PO BOX 80, SABULA, IA 52070-0080
PO BOX 81, SABULA, IA 52070-0081
PO BOX 82, SABULA, IA 52070-0082
PO BOX 83, SABULA, IA 52070-0083
PO BOX 84, SABULA, IA 52070-0084
PO BOX 85, SABULA, IA 52070-0085
PO BOX 86, SABULA, IA 52070-0086
PO BOX 87, SABULA, IA 52070-0087
PO BOX 88, SABULA, IA 52070-0088
PO BOX 89, SABULA, IA 52070-0089
PO BOX 90, SABULA, IA 52070-0090
PO BOX 91, SABULA, IA 52070-0091
PO BOX 92, SABULA, IA 52070-0092
PO BOX 93, SABULA, IA 52070-0093
PO BOX 94, SABULA, IA 52070-0094
PO BOX 95, SABULA, IA 52070-0095
PO BOX 96, SABULA, IA 52070-0096
PO BOX 97, SABULA, IA 52070-0097
PO BOX 98, SABULA, IA 52070-0098
PO BOX 99, SABULA, IA 52070-0099
PO BOX 100, SABULA, IA 52070-0100
PO BOX 101, SABULA, IA 52070-0101
PO BOX 102, SABULA, IA 52070-0102
PO BOX 103, SABULA, IA 52070-0103
PO BOX 104, SABULA, IA 52070-0104
PO BOX 105, SABULA, IA 52070-0105
PO BOX 106, SABULA, IA 52070-0106
PO BOX 107, SABULA, IA 52070-0107
PO BOX 108, SABULA, IA 52070-0108
PO BOX 109, SABULA, IA 52070-0109
PO BOX 110, SABULA, IA 52070-0110
PO BOX 111, SABULA, IA 52070-0111
PO BOX 112, SABULA, IA 52070-0112
PO BOX 113, SABULA, IA 52070-0113
PO BOX 114, SABULA, IA 52070-0114
PO BOX 115, SABULA, IA 52070-0115
PO BOX 116, SABULA, IA 52070-0116
PO BOX 117, SABULA, IA 52070-0117
PO BOX 118, SABULA, IA 52070-0118
PO BOX 119, SABULA, IA 52070-0119
PO BOX 120, SABULA, IA 52070-0120
PO BOX 121, SABULA, IA 52070-0121
PO BOX 122, SABULA, IA 52070-0122
PO BOX 123, SABULA, IA 52070-0123
PO BOX 124, SABULA, IA 52070-0124
PO BOX 125, SABULA, IA 52070-0125
PO BOX 126, SABULA, IA 52070-0126
PO BOX 127, SABULA, IA 52070-0127
PO BOX 128, SABULA, IA 52070-0128
PO BOX 129, SABULA, IA 52070-0129
PO BOX 130, SABULA, IA 52070-0130
PO BOX 131, SABULA, IA 52070-0131
PO BOX 132, SABULA, IA 52070-0132
PO BOX 133, SABULA, IA 52070-0133
PO BOX 134, SABULA, IA 52070-0134
PO BOX 135, SABULA, IA 52070-0135
PO BOX 136, SABULA, IA 52070-0136
PO BOX 137, SABULA, IA 52070-0137
PO BOX 138, SABULA, IA 52070-0138
PO BOX 139, SABULA, IA 52070-0139
PO BOX 140, SABULA, IA 52070-0140
PO BOX 141, SABULA, IA 52070-0141
PO BOX 142, SABULA, IA 52070-0142
PO BOX 143, SABULA, IA 52070-0143
PO BOX 144, SABULA, IA 52070-0144
PO BOX 145, SABULA, IA 52070-0145
PO BOX 146, SABULA, IA 52070-0146
PO BOX 147, SABULA, IA 52070-0147
PO BOX 148, SABULA, IA 52070-0148
PO BOX 149, SABULA, IA 52070-0149
PO BOX 150, SABULA, IA 52070-0150
PO BOX 151, SABULA, IA 52070-0151
PO BOX 152, SABULA, IA 52070-0152
PO BOX 153, SABULA, IA 52070-0153
PO BOX 154, SABULA, IA 52070-0154
PO BOX 155, SABULA, IA 52070-0155
PO BOX 156, SABULA, IA 52070-0156
PO BOX 157, SABULA, IA 52070-0157
PO BOX 158, SABULA, IA 52070-0158
PO BOX 159, SABULA, IA 52070-0159
PO BOX 160, SABULA, IA 52070-0160
PO BOX 161, SABULA, IA 52070-0161
PO BOX 162, SABULA, IA 52070-0162
PO BOX 163, SABULA, IA 52070-0163
PO BOX 164, SABULA, IA 52070-0164
PO BOX 165, SABULA, IA 52070-0165
PO BOX 166, SABULA, IA 52070-0166
PO BOX 167, SABULA, IA 52070-0167
PO BOX 168, SABULA, IA 52070-0168
PO BOX 169, SABULA, IA 52070-0169
PO BOX 170, SABULA, IA 52070-0170
PO BOX 171, SABULA, IA 52070-0171
PO BOX 172, SABULA, IA 52070-0172
PO BOX 173, SABULA, IA 52070-0173
PO BOX 174, SABULA, IA 52070-0174
PO BOX 175, SABULA, IA 52070-0175
PO BOX 176, SABULA, IA 52070-0176
PO BOX 177, SABULA, IA 52070-0177
PO BOX 178, SABULA, IA 52070-0178
PO BOX 179, SABULA, IA 52070-0179
PO BOX 180, SABULA, IA 52070-0180
PO BOX 181, SABULA, IA 52070-0181
PO BOX 182, SABULA, IA 52070-0182
PO BOX 183, SABULA, IA 52070-0183
PO BOX 184, SABULA, IA 52070-0184
PO BOX 185, SABULA, IA 52070-0185
PO BOX 186, SABULA, IA 52070-0186
PO BOX 187, SABULA, IA 52070-0187
PO BOX 188, SABULA, IA 52070-0188
PO BOX 189, SABULA, IA 52070-0189
PO BOX 190, SABULA, IA 52070-0190
PO BOX 191, SABULA, IA 52070-0191
PO BOX 192, SABULA, IA 52070-0192
PO BOX 193, SABULA, IA 52070-0193
PO BOX 194, SABULA, IA 52070-0194
PO BOX 195, SABULA, IA 52070-0195
PO BOX 196, SABULA, IA 52070-0196
PO BOX 197, SABULA, IA 52070-0197
PO BOX 198, SABULA, IA 52070-0198
PO BOX 199, SABULA, IA 52070-0199
PO BOX 200, SABULA, IA 52070-0200
PO BOX 201, SABULA, IA 52070-0201
PO BOX 202, SABULA, IA 52070-0202
PO BOX 203, SABULA, IA 52070-0203
PO BOX 204, SABULA, IA 52070-0204
PO BOX 205, SABULA, IA 52070-0205
PO BOX 206, SABULA, IA 52070-0206
PO BOX 207, SABULA, IA 52070-0207
PO BOX 208, SABULA, IA 52070-0208
PO BOX 209, SABULA, IA 52070-0209
PO BOX 210, SABULA, IA 52070-0210
PO BOX 211, SABULA, IA 52070-0211
PO BOX 212, SABULA, IA 52070-0212
PO BOX 213, SABULA, IA 52070-0213
PO BOX 214, SABULA, IA 52070-0214
PO BOX 215, SABULA, IA 52070-0215
PO BOX 216, SABULA, IA 52070-0216
PO BOX 217, SABULA, IA 52070-0217
PO BOX 218, SABULA, IA 52070-0218
PO BOX 219, SABULA, IA 52070-0219
PO BOX 220, SABULA, IA 52070-0220
PO BOX 221, SABULA, IA 52070-0221