Dangerous - Previewing the email alone is enough to infect your email.

Luckily , Microsoft has provided a temporary fix so, please apply ASAP. 

According to the article:- 

Although Microsoft states that the targeted attacks it has seen so far have been directed at users of its Word 2010 product, it’s clear that the remote code execution flaw also exists in Microsoft Word 2003, 2007, 2013, as well as Office for Mac 2011.

Microsoft Outlook 2007, 2010 and 2013 all use Word by default as the email reader.

The links below has more information:

http://grahamcluley.com/2014/03/rtf-wtf-microsoft-warns-word-zero-day-flaw-actively-exploited-targeted-attacks

My Yesterday's Blog

http://martin-news-bytes.blogspot.com/2014/03/interim-solution-temp-fix-available-for.html