During which time period do both PARS and CFS return mail to the sender?

The correct answer is associated with the last six months of the 18-month forwarding period, during which both the Postal Address Recognition System (PARS) and Centralized Forwarding System (CFS) processes are allowed to return mail back to the sender.

During the initial part of the 18-month forwarding period, the systems focus on redirecting mail to the new address rather than returning it to the sender. However, in the last six months, if the intended recipient does not update their address or fails to claim their forwarded mail, the systems will return the mail to the original sender. This is a crucial phase designed to ensure that mail is not indefinitely forwarded without proper attention to address updates.

This mechanism helps maintain the integrity of mail delivery services and ensures that senders are not left in a prolonged state of uncertainty regarding their correspondence. It is a significant part of the forwarding policy that balances service to both the sender and the recipient.