Whenever any amount due for the use of any box of any company shall remain unpaid for a period of one year, the company may, at the expiration of such period, send to the lessee of the box a notice in writing by registered or certified mail, postage prepaid, at his last known post-office address, notifying the lessee that if the amount due for the rental of the box is not paid within 60 days from the date of sending the notice, the company will cause the box to be opened and the contents thereof to be inventoried, sealed, and placed in one of the general safes or boxes of the company.