Hello.
I got a note that some of the senders (not all though), get the following error after sending their emails:
A message that you sent could not be delivered to one or more of its 
  recipients. This is a permanent error. The following address(es) failed:        
G@nospam.com       unrouteable mail domain "nospam.com"     
val@nospam.com       unrouteable mail domain "nospam.com" 
------ This is a copy of the message, including all the headers. ------   
 Return-path: <
designer@nospampls.com> 
 Received: from [61.3.128.81] (helo=sita) 
      by host.nospampls.org with smtp (Exim 4.43) 
      id 1CU80j-0005si-KF; Tue, 16 Nov 2004 13:25:06 -0500 
 Date: Tue, 16 Nov 2004 23:58:19 +0500
It seems that the Exim MTA has a trouble routing. Can it be some anti-spam protection?
Any ideas regarding this problem?
Thanks in advance.