寄信時看到「5.3.1 Bad recipient address syntax」訊息?

寄信時看到「5.3.1 Bad recipient address syntax (RCPT TO: <略…>)」這類訊息,表示您寄信的收件人地址的格式錯誤,導致 SMTP 伺服器拒收,以下為常見的錯誤案例: