[Recipient address rejected user unknown in relay recipient table (in reply to rcpt to command) recipient address rejected user unknown in relay recipient table (in reply to rcpt to command), Dec 28, 2020 · : Recipient address rejected: User unknown in relay recipient table (in reply to RCPT TO command) 上記の例では、メールの エラーコード は「 550 」となり、 エラーメッセージ 「 Recipient address rejected: User unknown 」が原因のエラーということとなります。. The server rejected the sender address. ]