Publication 685 - Publication for Streamlined Mail Acceptance for Letters and Flats - Contents 6-2.1 Mail Preparation First-Class Mail, Periodicals, and USPS Marketing Mail letters and flats and BPM-barcode..." /> Publication 685 - Publication for Streamlined Mail Acceptance for Letters and Flats - Contents 6-2.1 Mail Preparation First-Class Mail, Periodicals, and USPS Marketing Mail letters and flats and BPM-barcode..." />