Subject: Undelivered Mail Returned to Sender

From: [email-masked] (Mail Delivery System)
Date: Tue, 12 Aug 2008 15:07:58 +0300 (EEST)

This is the mail system at host noc.ntu-kpi.kiev.ua.

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

<[email-masked]>: host comsys.ntu-kpi.kiev.ua[10.18.49.10] said:
    550 5.1.1 <[email-masked]>... User unknown (in reply to RCPT
    TO command)