Question: My CPU usage on my server is very high, and it seems to be originated from my mail server. What could be the problem?
Answer: If your mail server is sucking up valuable CPU power, there are a couple of possibilities, none of which are pleasant.
1. You or users on your server are getting a lot of emails, more than usual. Although it is possible that it is just a temporary thing, it could be a deliberate attack on your server.
2. Someone is sending spam from your server, using an open relay in your SMTP settings or exploiting a user’s account.
3. Your server is receiving a ridiculous amount of spam (i.e. spam attack). This could be an intentional attack or just a particularly bad day.
Usually, if the CPU upswing is substantial, you should be really concerned about your server’s security. Take a look at the mail server logs and see where the emails are originating and where they are being sent. Take note of IP addresses, user names, and any other useful information. If you cannot figure it out, you can take the data to a security expert who can help you solve the problem.