Most “pre-sort” mail - like monthly bills and advertisements - is handled by sub-contractors, so it might not be digitally archived.
But most personal mail is coded by the USPS, and scanned on both sides, either by computer or by a remote CRT operator.
I know that gets archived for system analysis, but I don't know for how long.
Its supposed to be archived for 31 days tied to the fluorescent ID tag on the rear.
All mail that is collected via mailbox is scanned on the front and back, not for sinister purposes but for computer automation/OCR ability. An AFCS 200 machine can process nearly 30,000 pieces of mail/hour. It scans it, determines the facing direction, cancels the stamp, sprays an ID tag on the rear for remote encoding purposes if the address can’t be OCRed, if it is, a barcode is sprayed on the front.
ALL presort mail is only scanned on the front by the DBCS processing machines, again, for automated sorting purposes. A DBCS 6 machine is capable of processing mail at 40,000 pieces/hour with this capability. With both OCR and barcode reading ability.
The intention was never sinister, but for raw speed and efficiency. The (supposed) 31 day archival was to allow for lost or delayed mailpieces to reenter the system and find their destination more quickly without going through manual sorting.
Your friendly, neighborhood, rightwing postal worker, who is not a member of the jerkwad union.