This could be as simple as the way your message sender typed the message if they added a few Carriage return strokes on their keyboard.
eg If they were typing the text in a "smaller" Window or different Screen resolution than yours then they might be filling up a line and entering a Carriage Return stroke.
If you open the message up in a Word document, or copy and paste it into Word, you should then be able to click the "Show/Hide" button on the toolbar and see where the sender put their Carriage return strokes.
If you can't see the Show/Hide button ( usually displayed to the left of the page size box ) then click on View / Toolbars and select "Standard"
The Show / Hide button has the same symbol that is used to display a Carriage return stroke - it looks like 2 vertical lines with a small semi circle top left.
This in itself won't fix the problem but it might at least explain what's going on !