These three technologies are often combined into one machine, known as the Culler-Facer-Canceller Machine.

Segregating, or culling, is the process of separating mixed mail into flats and packets. This is necessary because a machine can sort flats while packets need to be sorted manually.  This process also removes damaged or oddly shaped pieces of mail from the main stream.

Facing is when flats are aligned so that the side of the letter with stamps on it is facing upward. The mail is then further aligned so that the stamps are in the top-right corner. All of this is done with a stamp-detecting device that can determine where the stamps are on the envelope, and then flip and rotate the envelope accordingly. This process can also be used to sort mail by class.

Canceling equipment imprints the stamps with a postmark saying where and when the stamp was canceled.  Once a stamp has been canceled, it cannot be used again.