Are you using Word as your e-mail editor? If so:
In Word 2007: Office button>Word Options>Display, uncheck as appropriate
under "Always show these formatting marks.."
In earlier versions of Word: Tools>Options>View, see the "Formatting Marks"
section.
One other possibility: If you are not using Word as your e-mail editor, but
are using Outlook '07: Open a message, click Office button > Editor Options >
Display, uncheck formatting marks as appropriate.