The Mailer ID, or Mailer Identifier, also known as a MID, is a 6-digit or 9-digit numeric code contained in an Intelligent Mail Barcode (IMb).
The MID is assigned by the USPS to identify the specific business responsible for sending a mailing. The USPS assigns MIDs to Mail Owners, Mailing Agents and other service providers as requested.
The number of digits in an MID is determined by annual mail volume criteria. 6-digit MIDs are assigned to higher volume mailers, making available a larger range of possible sequence numbers. 9-digit MIDs are assigned to lower volume mailers.
Like the Delivery Point Zip Code and other bits of tracking and delivery information in an Intelligent Mail Barcode, the digits of a MID are represented graphically as a series of bars. All 6-digit MIDs begin with a digit from 0 to 8. All 9-digit IDs begin with the digit 9.
Outgoing mailpieces from printers like Allen Press use the Mailer Identifier(s) associated with that business. Customers whose publications include Business Replay Mail (BRM) cards or inserts must apply for their own unique MIDs which will be embedded in the Intelligent Mail Barcodes for those pieces. An MID can be obtained by accessing the Business Customer Gateway.