on or around the ground floor of the apartment building, a series of mailboxes are typically kept in a location accessible to the public and, thus, to the mail carrier. every unit typically gets its own mailbox with individual keys to it. some very large apartment buildings with a full-time staff may take mail from the carrier and provide mail-sorting service. near the mailboxes or some other location accessible by outsiders, a buzzer (equivalent to a doorbell) may be available for each individual unit. in smaller apartment buildings such as two- or three-flats, or even four-flats, rubbish is often disposed of in trash containers similar to those used at houses. in larger buildings, rubbish is often collected in a common trash bin or dumpster. for cleanliness or minimizing noise, many lessors will place restrictions on tenants regarding smoking or keeping pets in an apartment.