To render well in most email clients VerticalResponse will force a line break at 72 characters in the Text version (as opposed to HTML) of your email. If your text ends right at 72 characters, on a given row, and you have your own line break you may see two breaks in the sent version of the Text email. To avoid this, make sure your Text email has line breaks before 72 characters; a 65 character width limit tends to work well in most email clients.
You may also find the Microsoft Outlook 2007 (and possibly other email clients) will disable line breaks by default. Click 'restore line breaks' in Outlook to show the line breaks in your email message.