What do different drop slots do in the USPS office?

Mail Drop Slot & Receptacle usps mail slot The USPS advises, If customers simply used retail service or inside wall drop slots to send their Mail, instead of depositing it to sit usps mail slot Per the USPS requirements, mail slot openings must be at least 1 ½ inches x 7 inches, and 30 inches above the floor Horizontal mail slots

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