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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.

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Ensure you are running a recent Linux/Unix distro. Every distro for the last several years has a default mailserver configuration that disables open relaying. You're not running the old Red Hat 7.3 are you? – Robin Green Apr 16 '11 at 6:54
up vote 1 down vote accepted

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.

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So they're coming from open relay? I'm not technical but afaik my friend has setup to block domain that's not in our list. – user78608 Apr 17 '11 at 16:46
Whoever is responsible for your mail server and the technical details needs to spend some time studying the proper ways to configure it for security. Your original question is quite broad so it's difficult to pinpoint a specific problem. Read the sendmail documentation (assuming that you are using sendmail). Return with questions as they come up. – colechristensen Apr 18 '11 at 4:58

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