。
Has the mailman been by yet?
Literal
Mail-person [topic-は] already come-[polite-past-ましたか]?
郵便屋 ('mailman, postman') is the familiar/casual term, built with the ~屋 suffix for occupation. The more formal counterparts are 郵便配達員 or 郵便配達人. もう + past tense asks about completion, parallel to English 'has he come already?' The さん-less form 郵便屋 is blunter than 郵便屋さん, fitting an in-house family conversation.