The Mail component in Apple iPhone OS 1.0 through 2.2.1 and iPhone OS for iPod touch 1.1 through 2.2.1 does not provide an option to disable remote image loading in HTML email, which allows remote attackers to determine the device address and when an e-mail is read via an HTML email containing an image URL.
https://exchange.xforce.ibmcloud.com/vulnerabilities/51209
http://www.vupen.com/english/advisories/2009/1621
http://www.securityfocus.com/bid/35434
http://www.securityfocus.com/bid/35414
http://support.apple.com/kb/HT3639
http://lists.apple.com/archives/security-announce/2009/Jun/msg00005.html