Am I under a DOS Attack?

Our domino server is getting hammered with what appears to be DOS attack 
(and it's handling it very well BTW).

I found miscellaneous events logs being generated every minute and mostly 
full of the same message:
10/13/2005 14:44:19   SMTP Server: Mail for mail_security@xxxxxxxxxxxxxxxx 
rejected for policy reasons.  Recipient could not be found in the Domino 
Directory.
10/13/2005 14:44:19   SMTP Server: Mail for mail_security@xxxxxxxxxxxxxxxx 
rejected for policy reasons.  Recipient could not be found in the Domino 
Directory.
10/13/2005 14:44:20   SMTP Server: Mail for mail_security@xxxxxxxxxxxxxxxx 
rejected for policy reasons.  Recipient could not be found in the Domino 
Directory.
10/13/2005 14:44:20   SMTP Server: Mail for mail_security@xxxxxxxxxxxxxxxx 
rejected for policy reasons.  Recipient could not be found in the Domino 
Directory.
This has been going on since around 1am on 11/11.
Doing a whois on fcep.net (identified by symantec secure mail for smtp) 
shows fcep.net as an electricy provider in China, who IMHO has been hacked 
and doesn't know they're being used as a spam relay.

Or I could be entirely wrong since I've not had any experience with 
anything like this.

Comments anyone?

Regards, Jerry

Gerald Kern
MIS Project Leader, Lotus Notes/Domino Administrator
IBM Certified RPG IV Developer, RPG IV Programmer
The Toledo Clinic, Inc.
4235 Secor Road
Toledo, OH 43623-4299
Phone 419-479-5535
gkern@xxxxxxxxxxxxxxxx