sub check {
  $_ = "sendmail[[text to be captured from sendmail],relaying denied";

  if (
    (/sendmail\[.*?\[(.*?)\],.*?Relaying denied/i) ||
    (/gnu-pop3d\[.*?refused connect from (.*?)$/i) ||
    (/cucipop\[.*?authentication failure\s.*?\s(.*?)$/i)
  ) { return ($1) };
  
  return "No match found";
};

print check,"\n";