Streets have had names for as long as there have been cities. Most early cities would have streets named for specific functions or businesses located there (e.g. "Butcher's Alley," "Market Street," or a few somewhat-vulgar appellations such as "Gropecunt Lane," a common name in Britain used to denote streets associated with prostitution). As for mail, in the era before widespread literacy this would rarely have been an issue - if you can't read, you're not getting any mail. Those who could read, normally influential figures of some sort or another, would be easy enough to locate by their houses, which would given their wealth and affluence be likely to stand out from the rest.