What happens to mail that cannot be delivered

When mail cannot be delivered, it's typically handled in one of the following ways:

1. Returned to sender: If the mail is undeliverable due to an incorrect or incomplete address, it's returned to the sender. The sender is usually notified through a "return to sender" label or a notice from the postal service.
2. Kept at the post office: If the mail is undeliverable due to a temporary issue, such as a missing mailbox or a resident being away, it's kept at the post office for a certain period (usually 30 days). If the issue is resolved, the mail is delivered. If not, it's returned to sender.
3. Donated or recycled: If the mail is undeliverable and cannot be returned to sender, it's often donated to charity or recycled. The postal service may partner with organizations to donate unclaimed mail to good causes, such as sending books to schools or hospitals.
4. Destroyed: In some cases, undeliverable mail may be destroyed if it's deemed to be of no value or if it's not possible to return it to sender. This is usually the case for mail that's been damaged, is no longer relevant, or contains sensitive information.
5. Sold at auction: In some countries, undeliverable mail may be sold at auction to collectors or enthusiasts. This is often the case for rare or unique items, such as stamps or coins.
6. Processed for data: Some undeliverable mail may be processed for data, such as extracting addresses or information for use in marketing or research purposes.

It's worth noting that the specific handling of undeliverable mail can vary depending on the country, postal service, and type of mail.