How do I configure Sendmail to use bl.0spam.org and rbl.0spam.org?

Follow these steps to configure bl.0spam.org and rbl.0spam.org in Sendmail:

1. Edit the Sendmail Configuration File

   Locate and edit the Sendmail configuration file, usually found at /etc/mail/sendmail.mc.

   Open the configuration file using your preferred text editor:

   sudo nano /etc/mail/sendmail.mc

2. Add the 0spam.org Blacklist and RBL Configuration

   Insert the following lines into your sendmail.mc configuration file to use bl.0spam.org and rbl.0spam.org as blacklists:

   FEATURE(`dnsbl', `bl.0spam.org', `Rejected - Listed on bl.0spam.org')dnl
   FEATURE(`dnsbl', `rbl.0spam.org', `Rejected - Listed on rbl.0spam.org')dnl
         

   This tells Sendmail to query bl.0spam.org and rbl.0spam.org and reject any incoming mail that is listed there, with the custom rejection message.

3. Rebuild the Sendmail Configuration

   After editing sendmail.mc, regenerate the sendmail.cf file by running the following command:

   sudo m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

4. Restart Sendmail

   Restart the Sendmail service to apply the new configuration:

   sudo systemctl restart sendmail

   If you're using an older system with init:

   sudo service sendmail restart

5. Verify the Configuration

   Check the mail logs, typically located in /var/log/maillog or /var/log/mail.log, to ensure the blacklists are functioning. Use this command to monitor the logs:

   tail -f /var/log/maillog

   Look for log entries indicating rejections:

   Rejected - Listed on bl.0spam.org
   Rejected - Listed on rbl.0spam.org