Campaign Monitor’s released their 2007 Guide to CSS Support in Email, a comprehensive study of CSS support by both desktop and webmail clients. This guide is an essential for anyone sending HTML mails out, especially in wide distribution as part of a mailing list or e-mail marketing.

It includes full breakdowns by client of what tags, selectors, and individual CSS properties are supported. Attention is paid to the new webmail services of the year — specifically Windows Live Mail which will be replacing Hotmail and the new Yahoo! Mail. The bad news on the desktop side is that Outlook 2007’s new e-mail rendering engine is pretty technologically backwards, and makes it nearly impossible to use CSS for even basic layout. The compatability charts are available as a PDF download as well.