The MobileMe component in Apple Mac OS X before 10.6.8 uses a cleartext HTTP session for the Mail application to read e-mail aliases, which allows remote attackers to obtain potentially sensitive alias information by sniffing the network.
http://www.securityfocus.com/bid/48444
http://support.apple.com/kb/HT4723
http://lists.apple.com/archives/security-announce/2011//Jun/msg00000.html