If you're using exim as your MTA you can set up a system filter to identify bounce messages for you. For example:

if error_message
then
  pipe "/usr/local/bin/handlescript"
  finish
endif
[download]

will pipe all bounce messages to your script and then discard them. That way your perl script only gets called for true bounce messages, which reduces the overhead.

If you want the bounced email to be delivered to the script but also to the original sender, just omit the "finish" keyword.