I'm currently running a Postfix mail server on CentOS 4.1 This morning our server started launching a DoS attack on *.hinet.net and *.tw domain names.

I've taken the server offline. But I really can't figure out the cause of the problem. Right now I have our old sendmail server running in its place. The sendmail server has all of the same users, but it is not experiencing the problem.

I've checked the maillog and it does not list the source of the emails (I was hoping for an IP or username). All it says is that the messages are coming from the queue manager.

How would I go about configuring Postfix to prevent it from sending DoS attacks to these two domains?

Thanks.

some more info:
The problem has got to be with the server itself. the server is no longer accessable from client machines and yet the problem is still there. Do you think reinstalling postfix would help? And if so, how could I go about beefing up security so this doesn't happen again?

Moved: This thread is more suitable in Linux - Security and has been moved accordingly to help your thread/question get the exposure it deserves.

Do you allow your postfix server to relay mail from the outside world to other outside world addresses?

Also, what do you mean by a DoS attack? Do you mean some kind of mail flood or is it un-related to the mail service?