+2  A: 

Yes, for example google gmail won't handle the STYLE element in the HEAD.

Look at this site for email clients and what they can/can't do regarding css: http://www.campaignmonitor.com/css/

Sydenam
+1 OK, so Gmail and the older versions of Lotus Notes do not support the STYLE element **at all**. Is there a reason (explanation) for Gmail being so backward in this issue? (Yahoo and Hotmail support it.)
Šime Vidas
Google puts in their documentation that it is because their UI relies heavily on stylesheets they do not support custom style sheets for emails. Here is the url http://mail.google.com/mail/help/accessibility.html and look in this section 'Section 1194.22 Web-based Internet Information and Applications'
Sydenam
+1  A: 

This might help

webb