Everybody know that using CSS in newsletter is tough. A lot of things just doesn’t work. Here is a list on what to use and not what to using concering stylesheets for HTML e-mails / newsletters. E.g. using background in newsletters is tricky. So check out here which readers will support it (e.g. Gmail and Outlook 2007 is pains in the …):
http://www.campaignmonitor.com/css/