This is the mail system at host mlsec231.city.fukuoka.lg.jp. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system : host 10.250.7.199[10.250.7.199] said: 550 5.1.1 : Recipient address rejected: User unknown in virtual mailbox table (in reply to RCPT TO command)