Final answer:
HTML e-mail can be dangerous due to potential malicious code, privacy concerns, and compatibility issues.
Step-by-step explanation:
HTML e-mail can be dangerous for several reasons. First, it can allow the launching of malicious code from the preview pane, which can potentially harm your computer or steal your personal information. Additionally, HTML e-mails can easily become public, as they can be forwarded, copied, or shared without your consent. Lastly, certain e-mail clients may not be able to properly display HTML e-mails, leading to compatibility issues.