How were letters delivered in the ancient world before street addresses?

Still sort of how it works in some parts of the world. My partner lived in Kathmandu and basically had to provide the same type of detailed description to point to a mailing address. "Go down that street, to the end of the street, until you see X, take a right, find the big red school building, ..." etc.

When she lived in rural Nepal she simply did not get mail at all.

She also often reflects on the technological steps that were simply skipped. Rural Nepal never got landlines and never will! No point.

Hoare’s Bank in London still gives its address as ‘at the sign of the golden bottle’ because that’s how addresses in England looked in 1672, when the bank was founded. Many buildings still only have names rather than numbers.

Some streets have fewer numbers than houses: https://youtu.be/Fr6Gxb97W_c

much of Costa Rica still doesn't have street addresses

The postie knew.

Arctic Canada has some great addresses. I worked for the telco that serves all of northern Canada , and in our provisioning and billing systems there are hundreds of addresses like “next to big blue house” or “down the road from post office”, because arctic First Nations town don’t (or didn’t) have street names and numbers.