Remediation Steps

Follow the steps below to remediate this finding on Linux (RHEL/CentOS/AlmaLinux).

1. For Postfix on RHEL/CentOS, edit /etc/postfix/main.cf:

   smtpd_relay_restrictions =
   permit_mynetworks,
   permit_sasl_authenticated,
   reject_unauth_destination

2. Restart Postfix:

   sudo systemctl restart postfix

3. For Sendmail, edit /etc/mail/sendmail.mc and ensure:

4. FEATURE(`access_db')

5. FEATURE(`blacklist_recipients')

6. Regenerate sendmail.cf:

   sudo make -C /etc/mail