FAQ After pulling my data into MAILERS+4, some of my ZIP Codes have only zeros in them. Why? Your ZIP Code field has been defined as a numeric-type field, which won't work for several reasons. Numeric fields are designed to carry numbers only, with no leading zeros. Your data may be truncated, or result in a decimal number. ZIP Code fields should be defined as a character-type fields to accommodate ZIPs that begin with zero as well as the dash when entering the 9 digit ZIP Code. Helpful Hint: When using a spreadsheet program like Microsoft Excel, be sure to format your ZIP Code column as Text rather than General or Numeric. This ensures proper transfer of your data.