Mail in Apple Mac OS X 10.4.11 and 10.5.1, when an SMTP account has been set up using Account Assistant, can use plaintext authentication even when MD5 Challenge-Response authentication is available, which makes it easier for remote attackers to sniff account activity.
https://exchange.xforce.ibmcloud.com/vulnerabilities/39104
http://www.vupen.com/english/advisories/2007/4238
http://www.us-cert.gov/cas/techalerts/TA07-352A.html
http://www.securityfocus.com/bid/26910
http://securitytracker.com/id?1019107
http://secunia.com/advisories/28136
http://lists.apple.com/archives/security-announce/2007/Dec/msg00002.html