Troubleshoot and resolve The system blocked a potential email loop. (WHMCS 8.4 and later) or Blocked Potential Email Loop (WHMCS 8.3 and earlier) errors.
Troubleshoot and resolve The sender's email address is not registered. (WHMCS 8.4 and later) or Unregistered Email Address (WHMCS 8.3 and earlier) errors.