In October 2006 USPS standard mailbox regulations for multi-tenant mailboxes were changed and must meet the security and configuration requirements of USPS STD-4C regulations. Some commercial mailboxes that are 4B+ compliant may be considered USPS approved if they are replacing existing mailboxes in an existing wall opening that will not be changed during renovations. We recommend getting postal approval for any 4B+ compliant commercial mailboxes before placing your order.