USPS introduced the ZIP+4 codes, also known today as “+4 codes”. ZIP+4 code is to add more precision to the standard five-digit ZIP codes.| PostGrid
There are several differences between the US and UK mailing address formats. It's crucial to follow the format to prevent any trouble.| PostGrid
The ‘USPS insufficient address’ meaning is that your mailing address is incorrect or incomplete in some way and it is undeliverable.| PostGrid
Canada's mailing address format is similar to the US ones, but addressing a letter to Canada is different from writing a domestic address.| PostGrid