Subject: Returned mail: see transcript for details

From: Mail Delivery Subsystem <[email-masked]>
Date: Tue, 23 Sep 2008 06:49:36 +0400

The original message was received at Tue, 23 Sep 2008 06:49:31 +0400
from [117.32.154.38]

   ----- The following addresses had permanent fatal errors -----
<[email-masked]>
    (reason: 550 <[email-masked]>, Recipient unknown)

   ----- Transcript of session follows -----
... while talking to rs1.rs-head.spb.ru.:
>>> RCPT To:<[email-masked]>
<<< 550 <[email-masked]>, Recipient unknown
550 5.1.1 <[email-masked]>... User unknown