Validates that the account Billing Zip/Postal Code is valid by looking up the first five characters of the value in a custom object called Zip_Code__c that contains a record for every valid zip code in the US. If the zip code is not found in the Zip_Code__c object, or the Billing State does not match the corresponding State_Code__c in the Zip_Code__c object, an error is displayed.
VLOOKUP(
$ObjectType.Zip_Code__c.Fields.City__c,
$ObjectType.Zip_Code__c.Fields.Name,
LEFT(BillingPostalCode, 5)) < > BillingCity