What GrandFather said, plus you have a couple of bad habits in there. You're apparently not using strict. Do it and warnings. Don't pass pre-formatted strings to an interface designed to accept data structures. Your "Cc" would be better as-

Let MIME::Lite sort out the way to join them. Though it's not crucial here, it's just a better habit, in some kinds of data formats it becomes crucial, and the general approach will lend itself to easier hacking.