>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

Yes, as those little things are to be more standardized in the way the source is built.

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

None that I know of.