Recently I've got problem from sending email out, it's about relaying denied. After doing some checking I found that my ip is being blacklisted, because of spamming. I checked my maillog and I found that my mail server has send lots email I did not send. But they got no recipient from, how they manage to send from my mail server? How do I trace out who is the spammer and what can I do to block them? I check the relay most of it either come from China, Thailand or Indonesia.
You have a security problem. You either left the door wide open or somebody broke in.
Make sure your server software is up to date, and take the time to thoroughly read sendmail's documentation. You could be hosting an open relay which leaves you wide open. No one, however, can give you specific steps to fix your problem because there are many possible things wrong.