HTML email in outlook
I'd suggest having a look at www.emailology.org. I've found it very useful when building emails for Outlook. As a rule for HTML emails, I build them purely in tables and with styles on the elements. It's horrible and like building bad websites years ago but unfortunatly it seems to be the best solution available.
For example, I'd change <p>
to <p style="font-family: Helvetica; font-size: 12px;">
and so on. Build it and style it like you would do normally but when you are happy enough to test it copy all the styles inline.
Have a look at Emailology though. It's a great resource.
This site provides a nice table overview (PDF download possible) of which CSS attributes will work with which email clients, what CSS selectors are supported, and where to define your CSS style (style tag vs. head style vs. inline):
http://www.campaignmonitor.com/css/
This post provides additional sources: https://stackoverflow.com/a/1019166/1143126
there are a huge number of guides out there that will help you with this as outlook is realy flaky with HTML, for example it dosent support nested 's which you are using.