Nothing grandiose, it's derived from "postmaster" (https://en.wikipedia.org/wiki/Postmaster_(computing) https://en.wikipedia.org/wiki/Postmaster_(computing)) —

Nothing grandiose, it's derived from "postmaster" (https://en.wikipedia.org/wiki/Postmaster_(computing) https://en.wikipedia.org/wiki/Postmaster_(computing)) — a person responsible for a mail server, which itself is borrowed from the IRL postmaster, a head of a post office. Likewise, "webmaster" is a person responsible for a web site.