Mail System Error - Returned Mail

[Mail Delivery Subsystem]

The original message was received at Wed, 7 Feb 2007 14:13:39 +0100
from linux.cz [70.85.196.39]

----- The following addresses had permanent fatal errors -----
<databases na linux.cz>

----- Transcript of session follows -----
... while talking to linux.cz.:
>>> MAIL From:"Mail Delivery Subsystem" <MAILER-DAEMON na linux.cz>
<<< 506 "Mail Delivery Subsystem" <MAILER-DAEMON na linux.cz>... Domain unknown