If you look at the content of the email, you'll see the following:
Code:
&=
nbsp; &nbs=
p; &=
nbsp; &nbs=
p; &=
nbsp; &nbs=
p; &=
nbsp;
Those are nonbreaking spaces. Zimbra's expressly not allowed to wrap them. Unfortunately, that's what the sender of the email seemed to want!
(The longest line in the message determines the width of the window we use to display it...)