Three options.
One: don't use text area's. Just use normal text boxes (no new lines allowed) instead.
But this is not too pretty, so:

Two: instead of thinging about $Message of a string of one line, read until you find a special line, for example: "#!#!END OF MESSAGE !#!#\n";
Everything, from the end of the message headers (author and such) of the message until that line should be considered the actual message.

Three: see the reply below. That one is even better!

Update: "added" an option :) © Happy-the-monk