You are not able to store more than 50 characters in the postalcode field, no matter what is configured in the user interface. To be clear, the user interface will let you enter a large field size (in your case 100) but the field in the underlying SQL database (CustomerAddressBase.PostalCode
) will not grow beyond 50, even if you customize the Address
entity to make the field size larger.
Not sure if this is intentional by design or a bug in Dynamics CRM, you would need to contact Microsoft to determine if it can be fixed. I can tell you that this does not appear to be documented anywhere in the CRM SDK documentation for the CustomerAddress entity.
I tested this in an on-premises installation and it has has the same issue.