De Por que minhas margens não funcionam no Outlook.com? :
Outlook.com no longer supports the following CSS properties: margin, margin-top, margin-right, margin-bottom, margin-left.
Replacing margin with padding on paragraph tags works well in Outlook.com, but Microsoft’s desktop clients didn’t fare so well: Outlook 2007/2010/2013 don’t support padding on block level elements.
Portanto, as margens funcionam na versão para desktop, mas o preenchimento não. E no preenchimento do Outlook.com funciona, mas não as margens. Portanto, uma solução de margens ou preenchimento só é possível se você e seus destinatários usarem apenas um dos tipos do Outlook.
Na extremidade, o artigo recomenda o uso de tabelas como a solução geral:
Use
<TD>
and swap margin for paddingPlacing each block of text or image inside its very own
<td>
cell — along with inline CSS padding — nets the best results across major email clients. While web development purists are rightfully hesitant to sully their emails with non-semantic markup, this method has worked well for us over the years. And while padding doesn’t work quite the same way as margin, it gets the job done. Just be especially careful when using borders, since you’ll need to play around with nesting tables to get your desired effect while relying solely on padding.