Retro Adress Postbox, Open Postal Mailbox. Flat Vector Icon illustration. Simple black symbol on white background. Retro Postbox, Open Postal Mailbox sign design template for web and mobile UI element. Retro Adress Postbox, Open Postal Mailbox. Flat Vector Icon illustration. Simple black symbol on white background. Retro Postbox, Open Postal Mailbox sign design template for web and mobile UI element.