($this_mail) # puts the value in a list context so that values captured by the regex are saved in the list (only the first match will be saved as there is only one variable available) 
            = 
              $this_in =~ # apply a regular expression to $this_in
                          /CN=(.*),CN=ExternalContacts/ # capture the bit in brackets
                                                     gio;  #apply globally (g), case insensitively (i) and only compile once (o)