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 4021, SAN MATEO, CA 94404-0021
PO BOX 4022, SAN MATEO, CA 94404-0022
PO BOX 4023, SAN MATEO, CA 94404-0023
PO BOX 4024, SAN MATEO, CA 94404-0024
PO BOX 4025, SAN MATEO, CA 94404-0025
PO BOX 4026, SAN MATEO, CA 94404-0026
PO BOX 4027, SAN MATEO, CA 94404-0027
PO BOX 4028, SAN MATEO, CA 94404-0028
PO BOX 4029, SAN MATEO, CA 94404-0029
PO BOX 4030, SAN MATEO, CA 94404-0030
PO BOX 4031, SAN MATEO, CA 94404-0031
PO BOX 4032, SAN MATEO, CA 94404-0032
PO BOX 4033, SAN MATEO, CA 94404-0033
PO BOX 4034, SAN MATEO, CA 94404-0034
PO BOX 4035, SAN MATEO, CA 94404-0035
PO BOX 4036, SAN MATEO, CA 94404-0036
PO BOX 4037, SAN MATEO, CA 94404-0037
PO BOX 4038, SAN MATEO, CA 94404-0038
PO BOX 4039, SAN MATEO, CA 94404-0039
PO BOX 4040, SAN MATEO, CA 94404-0040
PO BOX 4041, SAN MATEO, CA 94404-0041
PO BOX 4042, SAN MATEO, CA 94404-0042
PO BOX 4043, SAN MATEO, CA 94404-0043
PO BOX 4044, SAN MATEO, CA 94404-0044
PO BOX 4045, SAN MATEO, CA 94404-0045
PO BOX 4046, SAN MATEO, CA 94404-0046
PO BOX 4047, SAN MATEO, CA 94404-0047
PO BOX 4048, SAN MATEO, CA 94404-0048
PO BOX 4049, SAN MATEO, CA 94404-0049
PO BOX 4050, SAN MATEO, CA 94404-0050
PO BOX 4051, SAN MATEO, CA 94404-0051
PO BOX 4052, SAN MATEO, CA 94404-0052
PO BOX 4053, SAN MATEO, CA 94404-0053
PO BOX 4054, SAN MATEO, CA 94404-0054
PO BOX 4055, SAN MATEO, CA 94404-0055
PO BOX 4056, SAN MATEO, CA 94404-0056
PO BOX 4057, SAN MATEO, CA 94404-0057
PO BOX 4058, SAN MATEO, CA 94404-0058
PO BOX 4059, SAN MATEO, CA 94404-0059
PO BOX 4060, SAN MATEO, CA 94404-0060
PO BOX 4061, SAN MATEO, CA 94404-0061
PO BOX 4062, SAN MATEO, CA 94404-0062
PO BOX 4063, SAN MATEO, CA 94404-0063
PO BOX 4064, SAN MATEO, CA 94404-0064
PO BOX 4065, SAN MATEO, CA 94404-0065
PO BOX 4066, SAN MATEO, CA 94404-0066
PO BOX 4067, SAN MATEO, CA 94404-0067
PO BOX 4068, SAN MATEO, CA 94404-0068
PO BOX 4069, SAN MATEO, CA 94404-0069
PO BOX 4070, SAN MATEO, CA 94404-0070
PO BOX 4071, SAN MATEO, CA 94404-0071
PO BOX 4072, SAN MATEO, CA 94404-0072
PO BOX 4073, SAN MATEO, CA 94404-0073
PO BOX 4074, SAN MATEO, CA 94404-0074
PO BOX 4075, SAN MATEO, CA 94404-0075
PO BOX 4076, SAN MATEO, CA 94404-0076
PO BOX 4077, SAN MATEO, CA 94404-0077
PO BOX 4078, SAN MATEO, CA 94404-0078
PO BOX 4079, SAN MATEO, CA 94404-0079
PO BOX 4080, SAN MATEO, CA 94404-0080
PO BOX 4081, SAN MATEO, CA 94404-0081
PO BOX 4082, SAN MATEO, CA 94404-0082
PO BOX 4083, SAN MATEO, CA 94404-0083
PO BOX 4084, SAN MATEO, CA 94404-0084
PO BOX 4085, SAN MATEO, CA 94404-0085
PO BOX 4086, SAN MATEO, CA 94404-0086
PO BOX 4087, SAN MATEO, CA 94404-0087
PO BOX 4088, SAN MATEO, CA 94404-0088
PO BOX 4089, SAN MATEO, CA 94404-0089
PO BOX 4090, SAN MATEO, CA 94404-0090
PO BOX 4091, SAN MATEO, CA 94404-0091
PO BOX 4092, SAN MATEO, CA 94404-0092
PO BOX 4093, SAN MATEO, CA 94404-0093
PO BOX 4094, SAN MATEO, CA 94404-0094
PO BOX 4095, SAN MATEO, CA 94404-0095
PO BOX 4096, SAN MATEO, CA 94404-0096
PO BOX 4097, SAN MATEO, CA 94404-0097
PO BOX 4098, SAN MATEO, CA 94404-0098
PO BOX 4099, SAN MATEO, CA 94404-0099
PO BOX 4100, SAN MATEO, CA 94404-0100
PO BOX 4101, SAN MATEO, CA 94404-0101
PO BOX 4102, SAN MATEO, CA 94404-0102
PO BOX 4103, SAN MATEO, CA 94404-0103
PO BOX 4104, SAN MATEO, CA 94404-0104
PO BOX 4105, SAN MATEO, CA 94404-0105
PO BOX 4106, SAN MATEO, CA 94404-0106
PO BOX 4107, SAN MATEO, CA 94404-0107
PO BOX 4108, SAN MATEO, CA 94404-0108
PO BOX 4109, SAN MATEO, CA 94404-0109
PO BOX 4110, SAN MATEO, CA 94404-0110
PO BOX 4111, SAN MATEO, CA 94404-0111
PO BOX 4112, SAN MATEO, CA 94404-0112
PO BOX 4113, SAN MATEO, CA 94404-0113
PO BOX 4114, SAN MATEO, CA 94404-0114
PO BOX 4115, SAN MATEO, CA 94404-0115
PO BOX 4116, SAN MATEO, CA 94404-0116
PO BOX 4117, SAN MATEO, CA 94404-0117
PO BOX 4118, SAN MATEO, CA 94404-0118
PO BOX 4119, SAN MATEO, CA 94404-0119
PO BOX 4120, SAN MATEO, CA 94404-0120
PO BOX 4121, SAN MATEO, CA 94404-0121
PO BOX 4122, SAN MATEO, CA 94404-0122
PO BOX 4123, SAN MATEO, CA 94404-0123
PO BOX 4124, SAN MATEO, CA 94404-0124
PO BOX 4125, SAN MATEO, CA 94404-0125
PO BOX 4126, SAN MATEO, CA 94404-0126
PO BOX 4127, SAN MATEO, CA 94404-0127
PO BOX 4128, SAN MATEO, CA 94404-0128
PO BOX 4129, SAN MATEO, CA 94404-0129
PO BOX 4130, SAN MATEO, CA 94404-0130
PO BOX 4131, SAN MATEO, CA 94404-0131
PO BOX 4132, SAN MATEO, CA 94404-0132
PO BOX 4133, SAN MATEO, CA 94404-0133
PO BOX 4134, SAN MATEO, CA 94404-0134
PO BOX 4135, SAN MATEO, CA 94404-0135
PO BOX 4136, SAN MATEO, CA 94404-0136
PO BOX 4137, SAN MATEO, CA 94404-0137
PO BOX 4138, SAN MATEO, CA 94404-0138
PO BOX 4139, SAN MATEO, CA 94404-0139
PO BOX 4140, SAN MATEO, CA 94404-0140
PO BOX 4141, SAN MATEO, CA 94404-0141
PO BOX 4142, SAN MATEO, CA 94404-0142
PO BOX 4143, SAN MATEO, CA 94404-0143
PO BOX 4144, SAN MATEO, CA 94404-0144
PO BOX 4145, SAN MATEO, CA 94404-0145
PO BOX 4146, SAN MATEO, CA 94404-0146
PO BOX 4147, SAN MATEO, CA 94404-0147
PO BOX 4148, SAN MATEO, CA 94404-0148
PO BOX 4149, SAN MATEO, CA 94404-0149
PO BOX 4150, SAN MATEO, CA 94404-0150
PO BOX 4151, SAN MATEO, CA 94404-0151
PO BOX 4152, SAN MATEO, CA 94404-0152
PO BOX 4153, SAN MATEO, CA 94404-0153
PO BOX 4154, SAN MATEO, CA 94404-0154
PO BOX 4155, SAN MATEO, CA 94404-0155
PO BOX 4156, SAN MATEO, CA 94404-0156
PO BOX 4157, SAN MATEO, CA 94404-0157
PO BOX 4158, SAN MATEO, CA 94404-0158
PO BOX 4159, SAN MATEO, CA 94404-0159
PO BOX 4160, SAN MATEO, CA 94404-0160
PO BOX 4161, SAN MATEO, CA 94404-0161
PO BOX 4162, SAN MATEO, CA 94404-0162
PO BOX 4163, SAN MATEO, CA 94404-0163
PO BOX 4164, SAN MATEO, CA 94404-0164
PO BOX 4165, SAN MATEO, CA 94404-0165
PO BOX 4166, SAN MATEO, CA 94404-0166
PO BOX 4167, SAN MATEO, CA 94404-0167
PO BOX 4168, SAN MATEO, CA 94404-0168
PO BOX 4169, SAN MATEO, CA 94404-0169
PO BOX 4170, SAN MATEO, CA 94404-0170
PO BOX 4171, SAN MATEO, CA 94404-0171
PO BOX 4172, SAN MATEO, CA 94404-0172
PO BOX 4173, SAN MATEO, CA 94404-0173
PO BOX 4174, SAN MATEO, CA 94404-0174
PO BOX 4175, SAN MATEO, CA 94404-0175
PO BOX 4176, SAN MATEO, CA 94404-0176
PO BOX 4177, SAN MATEO, CA 94404-0177
PO BOX 4178, SAN MATEO, CA 94404-0178
PO BOX 4179, SAN MATEO, CA 94404-0179
PO BOX 4180, SAN MATEO, CA 94404-0180
PO BOX 4181, SAN MATEO, CA 94404-0181
PO BOX 4182, SAN MATEO, CA 94404-0182
PO BOX 4183, SAN MATEO, CA 94404-0183
PO BOX 4184, SAN MATEO, CA 94404-0184
PO BOX 4185, SAN MATEO, CA 94404-0185
PO BOX 4186, SAN MATEO, CA 94404-0186
PO BOX 4187, SAN MATEO, CA 94404-0187
PO BOX 4188, SAN MATEO, CA 94404-0188
PO BOX 4189, SAN MATEO, CA 94404-0189
PO BOX 4190, SAN MATEO, CA 94404-0190
PO BOX 4191, SAN MATEO, CA 94404-0191
PO BOX 4192, SAN MATEO, CA 94404-0192
PO BOX 4193, SAN MATEO, CA 94404-0193
PO BOX 4194, SAN MATEO, CA 94404-0194
PO BOX 4195, SAN MATEO, CA 94404-0195
PO BOX 4196, SAN MATEO, CA 94404-0196
PO BOX 4197, SAN MATEO, CA 94404-0197
PO BOX 4198, SAN MATEO, CA 94404-0198
PO BOX 4199, SAN MATEO, CA 94404-0199
PO BOX 4200, SAN MATEO, CA 94404-0200
PO BOX 4201, SAN MATEO, CA 94404-0201
PO BOX 4202, SAN MATEO, CA 94404-0202
PO BOX 4203, SAN MATEO, CA 94404-0203
PO BOX 4204, SAN MATEO, CA 94404-0204
PO BOX 4205, SAN MATEO, CA 94404-0205
PO BOX 4206, SAN MATEO, CA 94404-0206
PO BOX 4207, SAN MATEO, CA 94404-0207
PO BOX 4208, SAN MATEO, CA 94404-0208
PO BOX 4209, SAN MATEO, CA 94404-0209
PO BOX 4210, SAN MATEO, CA 94404-0210
PO BOX 4211, SAN MATEO, CA 94404-0211
PO BOX 4212, SAN MATEO, CA 94404-0212
PO BOX 4213, SAN MATEO, CA 94404-0213
PO BOX 4214, SAN MATEO, CA 94404-0214
PO BOX 4215, SAN MATEO, CA 94404-0215
PO BOX 4216, SAN MATEO, CA 94404-0216
PO BOX 4217, SAN MATEO, CA 94404-0217
PO BOX 4218, SAN MATEO, CA 94404-0218
PO BOX 4219, SAN MATEO, CA 94404-0219
PO BOX 4220, SAN MATEO, CA 94404-0220
PO BOX 4221, SAN MATEO, CA 94404-0221