Do you know what your United States Postal Service® (USPS®) account number is? Hmmmm – what exactly “IS” a USPS account number? Is it my Mailer Identification (MID) number? Is it my Customer Registration Identification (CRID) number?
Is it my postal permit number? If you are now scratching your head in puzzlement, you are not alone!
These account numbers are actually tied to postal permits and serve, at least in part, as a means for the USPS to identify the postage funding source.
Read more: http://www.windowbook.com/Learning/Postal-Concierge-E-tips