CSA = Customer Supplier Agreement - A CSA confirms the Origin-Entry preparation requirements and the acceptance window times necessary for mail to be considered entered into the postal network on "Start-the-clock Day Zero" Day-0 represents the date a mailpiece enters the mailstream and the date when the clock starts for purposes of service performance measurement. A CSA typically also include a schedule of transportation times, mail containerization specifications, designated postal mail facility entry locations, and time-sensitive mail entry instructions. However, a CSA does not create any service guarantee from the USPS.

    A CSA is required in any of the following situations:
    > Mailers who have their Origin-Entered mail verified at a Detached Mail Unit (DMU) and transported by USPS transportation
    > Mailers who prepare First-Class separations not covered in the DMM, is verified at a DMU, and transported on mailer transportation
    > Mailers who want to enter mail after a Business Mail Entry Units (BMEU) critical acceptance time,
    > Mailers who have volumes that require multiple dispatches to the BMEU

    CAT and CET = Critical Acceptance Time and Critical Entry Time. Both of these are used in conjunction with a CSA, and are for Service Performance Reporting purposes.

    Critical Acceptance Time is the latest time mail can be presented to have that day considered to be Day-0.

    Critical Entry Time is the latest time that a reasonable amount of a class of mail can be received at the platform at designated induction points in the postal network for it to be processed and dispatched in time to meet service standards.

    Reference - A Guide to Customer Supplier Agreements