From Longman Dictionary of Contemporary Englishpostmistresspost‧mis‧tress /ˈpəʊstˌmɪstrɪs $ ˈpoʊst-/ noun [countable] old-fashioned TCMa woman who is in charge of a post office → postmaster
Examples from the Corpus
postmistress• Bowing out: Myrtle Milner is retiring as postmistress in the village of Wharram-le-Street, near Malton.• Raybrock, Mrs, postmistress of Steepways.• Belle is the postmistress for the town, and it seems her work is never done.• She was postmistress of Oxford at the end of her life. 