I recently solved a similar problem. I am using cfsavecontent to send an html table with grouping. whenever I tried to use css I "lost" all of my styling. in order to get it to work, I created a <head> tag and used <cfinclude template="email.css">
<cfmail
to="#RecipientAddress#"
from="#SenderAddress#"
subject="#EmailSubject#"
type="HTML">
<HTML>
<head>
<style type="text/css">
<cfinclude template="/email.css">
</style>
</head>
<body>
<cfoutput>
#cfsavecontentvariable#
</cfoutput>
</body>
</HTML>
</cfmail>
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