Information:

MailStream Plus (MSP) was incorrectly recognizing the invalid ZIP Code 11111 (or other invalid ZIP Codes) as a valid one. The validation behavior of MSP regarding ZIP Codes is determined by position 28 of the ZIP IN parameter.

If position 28 of the ZIP IN parameter is blank, only the first three digits of the input ZIP Code are validated:

• Y: MSP checks all five digits of the input ZIP Code.
• N: MSP only checks the first three digits (default behavior when position 28 is blank).

Although 11111 is not a valid five-digit ZIP Code, there are valid ZIP Codes that start with 111, such as 11101, 11102, and so on. In the specific job mentioned, the ZIP IN position 28 was blank, causing MSP to only validate the first three digits.

Once position 28 was changed to Y, MSP recognized 11111 as an invalid ZIP Code because it considered all five digits for validation.