Extra line spacing in Plain Text email in Outlook

[Amy]

I use plain text as my default format for new emai messages. However,
whenever I open a new email message to compose, there is extra line spacing
whenever I enter text, and it also appears in my signatures. This happens
only when I've select ed MS Word as my editor. How do I remove the extra line
spacing under Plain Text without turning off the option to use MS Word as the
editor? I do not see Plain Text in the list of styles in the template.

I am aware of the Actions/New Message Using/Microsoft Outlook (Plain Text)
but how do I make this the default, without having to select it each time I
need to compose a new message?

Thanks for any help you can give.