What do different drop slots do in the USPS office?

Mail Slot, Sleeve, & Collection Box Combo mail drop slot Mail drop slots flip open when mail is delivered and chutes are angled slightly to direct the mail down and through the wall or door Check them out today! mail slot for wall Each letterbox requires a mail slot for doors where anyone passing by can notice where to drop in the mails These should be of the perfect size so as to

mail slot for front door The Mail Slot Sleeve was developed to cover the edges of exterior door openings and prevent mail from falling into hollow core doors