Not, as Outlook does, remove line breaks at will. If I send an email with line breaks in, there's a reason. For example: if my christmas list reads...

Magazines: This, that, t'other.
Teapot
Toolbox

Then that's the way I want to send my email, and the way it should be read. No one should have to wonder if I've discovered a magazine called "Teapot toolbox" and start looking for it. But my parent did wonder, thanks to these "feature" of Outlook.

Pah!

If only I were making this stuff up, it might even be slightly funny...