All new residential or commercial developments constructed after the enactment of the regulations contained in this chapter, except developments in R-1 and R-2 Residence Districts, and which are situated on any public street, avenue, or other roadway that is maintained by the city and receive curbside delivery of mail shall have cluster-style mailboxes. Any housing development constructed and already receiving mail service before the regulations in this chapter are enacted is not required to have cluster-style mailboxes.