The whole problem with Outlook and HTML code not being compatible started in 2007. Then, it has been hard to create a newsletter, since most HTML newsletters generate bugs in Outlook 2007. And, this is a huge problem, because nowadays most business people use outlook as their work email.
Even though there has been many criticism involved with outlook 2007, because of the problem mentioned above, they announced they will be using the same engine.
So, my advice to you is that you always use our test feature, before sending out your Email Marketing Campaign, that is the only way you will make sure that there is not a problem with your newsletter, when being received by Microsoft Outlook.