CVE-2004-2226
Mozilla Mail 1.7.1 and 1.7.3, and Thunderbird before 0.9, when HTML-Mails is enabled, allows remote attackers to determine valid e-mail addresses via an HTML e-mail that references a Cascading Style Sheets (CSS) document on the attacker’s server.
Date published : 2005-07-17
http://archives.neohapsis.com/archives/fulldisclosure/2004-11/0070.html