For POSTNET, a check digit will automatically be added. The data length must be exactly 5, 6, 9, or 11 digits, excluding the checksum digit which is added automatically by the software. If you are uploading a data file for VDP use, you must make sure the field does not include the check digit, or the data will be truncated to a 5 digit zip code.
No letters, spaces or punctuation are allowed. Only numeric digits 0-9.
If you would like to experiment with how edoc will react to various entries for POSTNET and OneCode inputs, here is a test template: