Nope that didn't work for me.
I was using One Note and copied the text from One Note and pasted it straight into a new Apple Mail message. Interestingly the font that was carried over was from One Note, not the default font I have configured for Mail.
Thinking that might be the problem, I pasted the text from One Note into a pure text editor (Sublime Text 2). Copied and pasted from ST2 to the same Apple Mail message - still the same problem.
Then I exited the Email message (didn't save) and created a new message. I pasted the text from Sublime Text 2 into the new "clean" message. Wrapping returned to normal, AND the default font I use for emails was restored.
I figure something "extra" got copied over from One Note and corrupted the email message. Its possible its font related?
Who knows, that ANY of this stuff works is a miracle to me!