Packages, letters, or other items that were sent via postal or delivery services but were never picked up or delivered to the designated receiver are referred to as unclaimed mail. Inaccurate addresses, recipients moving without updating their location, or non-reaction to delivery notifications are common reasons for the accumulation of these things. Depending on postal laws, they might eventually be put up for sale, sent back to the sender, or disposed of if they are not claimed. Customers of mystery boxes are drawn to the unidentified contents and the backstories of each undelivered parcel, which has led to an increase in the practice of investigating unclaimed mail.