I like this reversal of logic in terms of separation (that is, making it so that you don't need to add additional logic in the view.

But, the doubled negatives is a bit hard to read. I suggest an application of De Morgan's to apply that negative into condition:

    $csubject = "" if ! $csubject || $cusbject =~ /Re.../

And that is easier to read since now there's only one negative to parse!