Subject: Returned mail: see transcript for details

From: Mail Delivery Subsystem <[email-masked]>
Date: Fri, 24 Oct 2008 12:11:02 +0400

The original message was received at Fri, 24 Oct 2008 12:10:55 +0400
from [121.27.77.43]

   ----- The following addresses had permanent fatal errors -----
<[email-masked]>
    (reason: 550 Unknown user)

   ----- Transcript of session follows -----
... while talking to mail.ttg.gazprom.ru.:
>>> DATA
<<< 550 Unknown user
550 5.1.1 <[email-masked]>... User unknown
<<< 503-All RCPT commands were rejected with this error:
<<< 503-Unknown user
<<< 503 Valid RCPT command must precede DATA