>>What is double spaced ? The code you listed or the content?
>
>The message is only a sample. The email I send are much longer than that. With the new version of Outlook, whenever it sees a P tag, this affects the layout of the email. The layout is good when reading it but if you reply to it and go back to adjust the content, you will see that the line spacing is doubled.
>
>The only way around that is to use BR everywhere there is a P tag. But, then again, OL and UL will end up in the same situation. It is not a common procedure to grab the previous content and work on it but I do it on a particular process where I have an application that generates the email for me, send it to me at first, so I can then adjust a few more things and send it as if I would have written it in the first place.

Firstly, I take back what I said about the br tag. Your usage is fine for HTML5 - but it still might be worth trying self-closing tags.
Also I'm not sure whether a p tag without a closing tag is valid in your HTML (http://www.w3.org/TR/html-markup/p.html).
And, to be HTML5 compliant, you need to be careful where you use br inside a p : http://www.w3.org/html/wg/drafts/html/master/text-level-semantics.html#the-br-element

But I think Outlook is a bit flaky on rendering HTML anyway - it may be that nothing can fix this.....