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If you run a website on a virtual host, you receive a lot of messages one day telling you that the user address sent does not exist. Or you receive warnings from your host provider about user complaining your site sending spam. However, you never actually sent these emails.

Why is this happening? It's often due to vulnerabilities caused by improper mail server configuration, which hackers exploit to send spam emails. 

How can you protect your email server from spam senders? Here are some tips.

  1. Add an SPF record for your domain to ensure that only the specified host addresses are approved sources of your mail. 
  2. Review all your email accounts and delete any that are not in use. Use a strong password for all your accounts.
  3. Additionally, regularly check the login records of all email accounts on the mail server logs. If you notice a login from any suspicious IP addresses, the account's password may have been brute forced. 
  4. Add protection to prevent hackers from brute-forcing your user accounts and passwords. A common tool for this is Fail2ban, which can automatically block hosts that repeatedly attempt to log in with wrong usernames and passwords multiple times. It can also help prevent malicious bots from exploiting website vulnerabilities.